Testing chambers for Lapua use............

Deeper has been Better

Good Morning Kevin,
I have been playing with the deeper chambers for the last five years. This year I went to using R50 and have really been impressed. Mike Cameron got me interested by finding a Lot that shot “lights out” in his Suhl barreled by Wayne Smith. Wayne’s chambers are deeper because of position shooters needing to be able to extract live rounds – I don’t know how much deeper. Well anyway, his guns with the deeper chambers have been killers, mine as well as, Mike Cameron’s won the IR 50/50 List shooting two of Wayne’s guns this year and there are several others. Jody Reed’s gun cleaned up last year shooting indoors, and you know all about how the Kempley’s shoot theirs.
This past Tuesday I shot a Turbo with a 6 groove Rock Creek barrel fitted by Gordon Eck – with a deeper chamber – Gordon and I are running an experiment using R50 against Eley. This was the second time I shot it, the first time just learning where to set the tuner (a very interesting story), on Tuesday I shot it playing with different ammo, the best Eley was 2119 at 1066 it shot ok, but I keep getting droppers and I went to R50 Lot 150 and I can see a bunch of promise in this barrel. I’ll see if I can find out from Gordon and Wayne how deep they are going and get back to you. I think you are on to something that can help us all.
Bob Collins
 
Bob:

I apologize for not keeping in touch with you - it has been a long time since we spoke (and I miss our conversations). You have helped me a LOT over the years, and I greatly appreciated it!

I would love to hear how Gordon and Wayne are setting them up - you know, we might just compile some information and figure some of this out after all!!

I have heard great things about the (new) R50 - Paul Gideon has tested it and provided me some cronograph information that was just amazing. Very promising stuff! Competition is a very good thing in the ammunition business (heck, ANY business), it pushes all of them to make better product.

I have a Rock Creek in the safe that I have tested with a 2 degree chamber in it - I will set it back this weekend (with a longer leade 1.5 degree) and let you know if it improves. I have a ton of tuner setup information on it as it currenty stands (I know all of it will be useless when the length changes - but it does form a general baseline for comparison).

I was squadded next to Tal and Reya this year - both were amazing (as always!). What Reya did in the iron sight phase was inspirational. I was very proud of her - and humbled every time we changed targets (clean thru the first two days of the Nationals)!

I would be VERY interested in your procedure when establishing tuner sweet spots - I have my own opinions, but I would love to hear yours (you and many others here have a LOT more experience with them than I).

Thanks for the post Bob - it's great to hear from you!

kev
 
Throat Dia.?

Great stuff! I've got a question that's been bugging me. The nominal bullet dia. of the .22RF is .222. We chamber with reamers of .224 to .226 so even with bullet engraving we have a "throat" if you will of two to four thousandths over bullet dia. leaving at least the back half of the bullet unsupported. I have never heard of any other cast bullet discipline that would chamber a rifle or pistol for that matter with that much clearance. Does anyone know of anyone trying a chamber with a short throat section of .222 just in front of the case? Seem this would limit bullet swaging on firing and align the bullet better.

Dennis
 
Dennis D. said:
Great stuff! I've got a question that's been bugging me. The nominal bullet dia. of the .22RF is .222. We chamber with reamers of .224 to .226 so even with bullet engraving we have a "throat" if you will of two to four thousandths over bullet dia. leaving at least the back half of the bullet unsupported. I have never heard of any other cast bullet discipline that would chamber a rifle or pistol for that matter with that much clearance. Does anyone know of anyone trying a chamber with a short throat section of .222 just in front of the case? Seem this would limit bullet swaging on firing and align the bullet better.

Dennis
Click to expand...

Dennis:

That's a great question!

I think that's why the conventional wisdom has always been the more engraving is always a good thing - and it makes sense (to support as much of the bullet as you can either engaged in the rifling, or in a minimum diameter throated section).

I have not tried what you suggest but I can say that the results were not good with heavy engraving (in my test barrels).

I would love to see someone try this though!

Thanks for the post,

kev
 
Well, I've got a Shilen polygon barrel that should be coming before long, once I get it I'll measure the bore and contact Dave Mason and see if he'll make me up a throating reamer. Now, any suggestions as to what the lead angle should be into the rifling? I'm leaning towards 2 degrees as I think that should work for both the poly and standard rifling. For the mouth of the case I'm torn between 2 or 3 degrees as I already have reamers for both. I'd like to keep that as short as possible to limit bullet bump-up just out of the case but I don't want to abrupt of a transition either. Suppose I could always start with 3 and just lengthen it later to 2 if it leads up at the mouth of the case.

Open for suggestions.
 
Most CZs shoot very well for what they are.........Most off them have a "tight" bore. Of coruse they are not match grade. BUT they do shoot I think this tight bore less engraveing on the bullet may be a reason.......
 
Hi Kevin,
I have to thank you for 'going off the reservation' with your chambering tests !
I just lengthened the chamber in one of my barrels after getting frustrated with its finicky characteristics. You know, shoot some .1 five shot groups and then start spraying for a while then settle back down for a while and repeat in the colder weather.
I never knew when Dr Jeckel or Mister Hyde was just around the corner. So far with three different lots of ammo everything shoots between .18 and .25 c-c for 10 shot groups. Not the propensity for the true one holer, but no zingers !!! It will also continue to shoot well with 75 to 100 rounds between cleaning and the amount of residue seems to be much less and greasier. It's working really well with just a little Iosso in the chamber and a couple dry patches. Thanks for giving me that little nudge to give it a try !!
- take care - Dave
 
The Shadow said:
Hi Kevin,
I have to thank you for 'going off the reservation' with your chambering tests !
I just lengthened the chamber in one of my barrels after getting frustrated with its finicky characteristics. You know, shoot some .1 five shot groups and then start spraying for a while then settle back down for a while and repeat in the colder weather.
I never knew when Dr Jeckel or Mister Hyde was just around the corner. So far with three different lots of ammo everything shoots between .18 and .25 c-c for 10 shot groups. Not the propensity for the true one holer, but no zingers !!! It will also continue to shoot well with 75 to 100 rounds between cleaning and the amount of residue seems to be much less and greasier. It's working really well with just a little Iosso in the chamber and a couple dry patches. Thanks for giving me that little nudge to give it a try !!
- take care - Dave
Click to expand...

Thanks Dave!

The weather here in NW Ohio is not giving me any windows for testing (that's for sure!). Can't wait to get back at it once the weather breaks.

Thanks a ton for sharing (good or bad) your results - I think the only way we can start to quantify some of this information is thru this process. Is the accuracy you noted raw (before tuning)..........if it is, that (IMHO) would be a great start. .180" c/c (and smaller) is not really easy to come by (consistantly).

Thanks again,

kev
 
I wish it was, but that's with the tuner set at my old setting on the short chamber. I've tried it at some different settings but it prefers the previous 1085 Match setting, so apples to apples it's much more confidence inspiring. Apparently it works for Eley as well as Lapua and RWS. Might be a little different dimensionally but the concept is the same.
- take care - Dave
 
Measuring OAL's

A couple of days ago I measures 7 boxes of a lot of ammo I have that shoots exceptionally well. I measred the ammo from the front of the driving band to the butt of the case. I measured 7-50 round boxes and got the following results: 5 boxes plus 19 rounds meaured .743, 1 box that measured .741, 30 rounds that measured .744 and 10 rounds that measure .742.

It is my suspision that good shooting lots will all measure up this way. I also suspect that each chamber will respond well or better to ammo that is within a certain OAL area, for lack of a better word. I am probably not the first to do this and I know there are guages out there to measure the OAL's.

I think this correlates to the engraving thing and /or the chamber length. Forcing a round into a chamber will create more pressure when fired than rounds that do not engrave as much. Some barrels require a very narrow amount of "jamming" to shoot well. I have seen it to be true with CF rifles. A very few barrels will shoot anything one feeds them but they are dern few, from my experience.

I also measurd the OAL's of a couple other lots that do not shoot well in the barrel that likes the lot I mentioned first. Their OAl's measured somewhat different than the first lot measured. It would be interesting to find a similar OAL to my good one in another lot of ammo and see if it is indeed the OAL that dictates tune. I will attempt to do that.

Perhaps a longer chamber is more forgiving with regard to ammo, in general, and tune than the shorter ones?
 
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Pete Wass said:
A couple of days ago I measures 7 boxes of a lot of ammo I have that shoots exceptionally well. I measred the ammo from the front of the driving band to the butt of the case. I measured 7-50 round boxes and got the following results: 5 boxes plus 19 rounds meaured .743, 1 box that measured .741, 30 rounds that measured .744 and 10 rounds that measure .742.

It is my suspision that good shooting lots will all measure up this way. I also suspect that each chamber will respond well or better to ammo that is within a certain OAL area, for lack of a better word. I am probably not the first to do this and I know there are guages out there to measure the OAL's.

I think this correlates to the engraving thing and /or the chamber length. Forcing a round into a chamber will create more pressure when fired than rounds that do not engrave as much. Some barrels require a very narrow amount of "jamming" to shoot well. I have seen it to be true with CF rifles. A very few barrels will shoot anything one feeds them but they are dern few, from my experience.

I also measurd the OAL's of a couple other lots that do not shoot well in the barrel that likes the lot I mentioned first. Their OAl's measured somewhat different than the first lot measured. It would be interesting to find a similar OAL to my good one in another lot of ammo and see if it is indeed the OAL that dictates tune. I will attempt to do that.

Perhaps a longer chamber is more forgiving with regard to ammo, in general, and tune than the shorter ones?
Click to expand...

Pete,
I'm not so sure that more engraving leads to more pressure. With a 'dead' lead bullet we are doing with bolt camming what the powder charge should be doing. Lead has no springback so the farther we push it into the rifling pre-ignition the less the powder has to do. Jumping the bullet will have the same effect. There must be a sweet spot that's a compromise between bullet alignment and combustion control for consistent bullet release. I know you're correct for CF jacketed bullets but I think RF is a different animal.
- take care - Dave
 
I'd sure want to run tests on the rims to see how much of that varience is rim thickness. How exactly do you measure from the drive band without making up a die to consistantly seat it in?
 
The Shadow said:
Pete,
I'm not so sure that more engraving leads to more pressure. With a 'dead' lead bullet we are doing with bolt camming what the powder charge should be doing. Lead has no springback so the farther we push it into the rifling pre-ignition the less the powder has to do. Jumping the bullet will have the same effect. There must be a sweet spot that's a compromise between bullet alignment and combustion control for consistent bullet release. I know you're correct for CF jacketed bullets but I think RF is a different animal.
- take care - Dave
Click to expand...

Typically I have found the best accuracy at .006" into the lands. Some barrels like .009 and the odd one will like .015. I have one of those but most of the .30 cal barrels I have owned have given the best goups at .006" into the lands.

My thinking is if a person could find ammo with consistent AOL's, find out what length chamber makes that ammo work well there is at least some way to be able to quantiy why some ammo and chambers work well together and some don't.

CF bullets are made from 100% lead and the jackets are quite delicate so I don't think there would be a lot of difference in their crushing and with only Jamming .006" we are talking something very light. I think it worth looking at anyway. I think regardless of what the bullet is made from, if one has to jam the cartridge hard to get the bolt closed, one has loaded more pressure into that round. If the bullets lightly lay into the lead there is less pressure created when the round goes off. I could be wrong. I've been wrong before.
 
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tim simbari said:
I'd sure want to run tests on the rims to see how much of that varience is rim thickness. How exactly do you measure from the drive band without making up a die to consistantly seat it in?
Click to expand...

I am using a dial vernier caliper with a Stoney Point comparitor clamped to one ot the jaws. I am able to accurately find AOL's with it. I use the same set up to measure OAL's with my CF rounds. It is as accurate as it needs to be to measure OAL's for the purposes we need . The nose of the bullet goes into the comparitor and rests on the face of driving band, the butt on the other jaw of the caliper.

I have considered the rim thickness and how, perhaps, a better and more accurate way to measure is from the front of the rim to the face of the driving band. There is a comparitor available that will do this I believe. I just don't know how much of an effect the rim thickness has on performance. According to the maker of the comparitor, one should sort by rim thickness first, of course they sell a rim thickness guage so - - --

I just got in some ammo to test. I went through it and typically I found about 25 or so rounds with the same OALs, 15 others .001"either larger or smaller, ten either larger or smaller than the other but all the same length and 4 that are yet another size and one that is WAAAY different.

Also, there is a distinct variation between machine numbers. Machine 6 seems to make longer Ammo than machine 2, for instance. Perhaps this is why some chambers like a particular machine's ammo over others. Perhaps this is a wild goose chase but I think it worth exploring.

PS: I just measured 10 rims with the calipers, which I don't think is the most accurate method but 9 measured .038" and one measured .037"
 
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WOW! What an interesting and instructive thread. I'd like to add a few thoughts, particularly in response to the Shadow's post #2.

First let me define a few terms that I need to use.
Engraving Force = the force needed to fully engrave the bullet in the bore
Bullet Pull = the force with which the cartridge case crimp holds the bullet in the case
Shot Start Force = the total force needed to unseat the bullet from the case and engrave it.

So, Shot Start Force = Engraving Force + Bullet Pull

In my opinion, Shot Start Force must be very uniform. And it must be high enough to cause uniform and complete burning of the propellant. If Shot Start Force is too low, the bullet will move forward too soon, increasing the volume in which the propellant is burning, reducing the propellant's burning efficiency and gas pressure. (I learned this the hard way when designing a rimfire conversion kit for the M16 Series Rifles).

If we cut our chambers so short that chambering the cartridge engraves too much of the bullet, there may not be enough remaining Engraving Force to assure adequate Shot Start Force.

The problem would be exacerbated by cartridges with particularly powerful primers and/or low bullet pulls. Powerful primers necessitate higher Shot Start Force because the primer itself can add significantly to the total shot start pressure. Low Bullet Pull necessitates higher Engraving Force to assure that total Shot Start Force is adequate.

And, if you see more residual propellant in the shorter chamber, perhaps that is indicative of inadequate Shot Start Force.

I'd suggest that the shorter chamber may offer better alignment of the projectile in the bore. However, it does so at the expense of engraving force. And, inadequate engraving force may decrease uniformity of propellant burning which may cause unacceptable variations in muzzle velocity.

Just trying to help.

Hawkeye Wizard
 
Hawkeye,
I think you explained it perfectly. Where you really notice it is when you slug a barrel. The highest resistance you meet is the initial push into the bore. Once it gets in even a small distance the resistance decreases. My spring checker doesn't go low enough with accuracy to really quantify the difference, but I'm sure it can be verified.
As regards residue, that's exactly what I've found by lengthening the chamber.
- take care - Dave
 
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