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

kevin nevius

Sharpshooter
Jan 6, 2011
473
155
Gibsonburg, Ohio
Hi everyone!

I thought I would pass along some recent testing information.

I have been experimenting this fall / winter trying to optimize the performance of the Lapua smallbore ammunition – specifically the chambering.

I have used several configurations since 2009, the most successful was (is) a 2 degree leade angle, set at a dimension of .600 from the contact face to the start of the leade. Of all the 2 degree leade chamber configurations I have tried, this was the optimum dimension for bullet engraving in all of the test barrels I have used. This dimension engraves just to the second band.

1.5 degree chambers have been the topic of conversation on several forums, so I purchased several 1.5 degree spiral reamers and began testing. The chamber I am using is the "Meyers" profile (with a very small amount of body taper, something I prefer). The “standard” setup dimension is .600”. The engraving is more pronounced due to the more shallow leade. I had always assumed more engraving was better (a carryover from developing HP loads with VLD bullets!), so I started testing at .580”. The results in all barrels were not promising – vertical dispersion even though the chronograph numbers looked reasonably good. I moved it out in .005” increments until I reached .620” and nothing looked exceptionally promising – so I stopped and pretty much gave up.

Last week I was revisiting a post from Dr. Kolbe (Border Barrels) regarding chambering, and he mentioned some success with less engraving. So………I started moving the leade out in my test barrels. When I reached .660”, results (in all barrels) improved dramatically. Engraving is just barely visible on the first band. The vertical disappeared, and groups became round (and small!).

I was always hesitant to move the leade out – I had always thought that the bullet deformation from the gas pressure should happen with as much of it (as possible)supported by the bore / rifling.

Food for thought (for those chambering with Lapua ammunition in mind).

PS - The testing is limited to (2) Hart barrels, a six groove and a two groove - hardly a large scientific sample, I know! I use a lot of Hart barrels mainly because of their consistent quality and internal dimension. Experimenting with them translates very well from barrel to barrel - so I am very hopeful of any positive results I see with them.

Just thought I would share,

Have a great Christmas all!

kev
 
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Hi Kevin,
Do you think that forcing the ignition pressure to do the engraving rather than the camming of the action has any bearing on this ? Have you noticed any difference in the residue after cleaning between the .580 and .660 chambers. This the key issue I'm wrestling with at the moment. Do you have an assortment of test barrels - MI and conventional ? Anything you've noticed is of great interest to me.
- take care - Dave
Working on my laptop and cut off the last of your post about the 2 Harts !
 
Last edited:
GOOD STUFF

Kevin, I'm delighted to see that you are back posting. You're Definitely a breath of fresh air. I'd love to see Lapau back on top. Best wishes
 
Hi Kevin,
Do you think that forcing the ignition pressure to do the engraving rather than the camming of the action has any bearing on this ? Have you noticed any difference in the residue after cleaning between the .580 and .660 chambers. This the key issue I'm wrestling with at the moment. Do you have an assortment of test barrels - MI and conventional ? Anything you've noticed is of great interest to me.
- take care - Dave
Working on my laptop and cut off the last of your post about the 2 Harts !

Something I read 20 years ago that is stuck in my mind as a possibility.....

Setting the leade farther out and letting the ignition pressure engrave the bullet can help because: When the bullet gets a bit of a "jump"- the hot gasses will pass the heavy bullet before the round has time to engrave. These hot gases tend to align/center the bullet with the bore.

In the back of my mind I tend to think there is something to this theory. Does anyone think there might be something here? :)
 
Dizzy,
I don't think having the gases leak by the bullet could have any positive effect. It would lead to vaporization of the lube and gas cutting of the bullet with the subsequent leading of the barrel. I don't think the .660 was actually allowing any jump. Kevin mentioned that it was just touching the front driving band.
- take care - Dave
 
Dizzy,
I don't think having the gases leak by the bullet could have any positive effect. It would lead to vaporization of the lube and gas cutting of the bullet with the subsequent leading of the barrel. I don't think the .660 was actually allowing any jump. Kevin mentioned that it was just touching the front driving band.
- take care - Dave

Thanks Dave for the reply, I had never thought of vaporization of the lube ect.....

What I was thinking: it takes a little less than .003 (3 thousandth) of a second for a bullet to clear a 24 inch barrel. I can't think small enough for the amount of time it would take for the bullet to move say .010 of an inch and seal the bore.

Can you please explain how that would enough time for the hot gas to vaporize the wax, and create a gas check and lead the barrel. Even with the gas being as hot as it is I would not be afraid to to expose my finger to this much heat in so short of time. (.010 of an inch).
 
Hello Kevin, thanks for sharing your chamber testing results using Lapua rimfire ammo. Very interesting information that deserves further testing using barrels from various companies.

As for the quality of Hart rimfire barrels? One only needs to look at the equipment list from the most recent ARA Indoor Nationals. Fourth, Seventh and Twelveth place were taken, shooting what appears to be the same rifle. Three different competitors using a "Hart" barrel and Eley ammo. Not to shabby!

Congrats to Fred Sears, his daughter and grand daughter on excellent shooting.

All the best, ... John
 
HI Dizzy,
I think it's more a matter of an exposed edge on the rebated section of the bullet being melted from the gases blowing by as opposed to bumping it to bore dimensions.
Have experienced this in BPCS while experimenting with different bullets and base wads.
It amazes me also that it can happen so quickly but the pressures and temps are pretty extreme for an unprotected bullet. You can see the same thing pretty readily in .45 autos shooting lead bullets without gas checks. For the most part I have found that undersize bullets lead worse than oversize. I think Lewis has sold a lot of lead removers because of this phenomenum !!
 
Fred's combination was definitely working in La. There were a lot of very good rifles and shooters having difficulties of one sort or another.
- take care - Dave
 
Great Info!

Richard and I was discussing this very thing the other nite,he change the depth of his chamber on a Shilen octogon and it seem to very positive for the MI barrel. Kevin ,maybe depth on certain rifleling has more positive effect than say the 4C or the Ratchet vs say a Octogon, Maybe Richard will post his thoughts on this.
 
I think you're on the right track Willy. I have a strong suspicion that barrels of different dims and land to groove ratios respond to different chamber configurations. I don't think there is a one size fits all.
- take care - Dave

I wonder if Kevin has tried Eley with these same chambers for a comparison ?
 
Hi Kevin,
Do you think that forcing the ignition pressure to do the engraving rather than the camming of the action has any bearing on this ? Have you noticed any difference in the residue after cleaning between the .580 and .660 chambers. This the key issue I'm wrestling with at the moment. Do you have an assortment of test barrels - MI and conventional ? Anything you've noticed is of great interest to me.
- take care - Dave
Working on my laptop and cut off the last of your post about the 2 Harts !

Hi Dave:

I think the camming force has a lot to do with it. When the chamber was initially cut at .580" the seating force was really high (very noticable). Much more so than the 2 degree leade - you are doing a lot more swaging with the more shallow leade!

I noticed no difference regarding cleaning - the chamber needs very few shots to settle in, and has (in these two barrels) maintained accuracy for extended shooting sessions (200+ rounds of testing / tuner setup).

I have a 16 twist Krieger and a 4 groove Benchmark MI in the shop now - those will be next. I think (??) the Harts would be considered MI - wouldn't they?

Hart barrels are very consistent when evaluating them - they only offer one internal dimension set for them (they are all VERY close to .2170 x .2215) - which makes setting up reamer stops pretty easy! (and makes the results fairly repeatable from barrel to barrel).

Thanks for the post!

kev
 
Kevin, I'm delighted to see that you are back posting. You're Definitely a breath of fresh air. I'd love to see Lapau back on top. Best wishes

Thanks for the post, I have really enjoyed the forum!

I admit I am certainly a novice - I just really enjoy playing with this cartridge! I started doing my own work (and some limited work for others) back in the late 90's - I just grew tired of waiting over a year to get a rifle built!!

Lapua is a sponsor,so I have spent the past few years doing some develpoment for them (and me!). The offerings from Lapua (and RWS) are, and have been very promising. Personally, I prefer the round nosed bullet - and believe (based on opinion and experience) that there is some benefit in the wind to this profile.

Thanks again,

kev
 
Something I read 20 years ago that is stuck in my mind as a possibility.....

Setting the leade farther out and letting the ignition pressure engrave the bullet can help because: When the bullet gets a bit of a "jump"- the hot gasses will pass the heavy bullet before the round has time to engrave. These hot gases tend to align/center the bullet with the bore.

In the back of my mind I tend to think there is something to this theory. Does anyone think there might be something here? :)

That's a great point - I don't think I would push the leade out beyond .660" (in these .2170 x .2215 barrels) for that reason.

At .660" - using a jewelers lope - you can see the defined band of the leade (about .020" back) so I don't believe there is any blow by at that point. The cronograph numbers are also very good (Lapua ammunition has very good numbers to begin with), they would certainly show some fluctuation if there was no established seat (I would think, anyways)?

Thanks for the post!

kev
 
Hello Kevin, thanks for sharing your chamber testing results using Lapua rimfire ammo. Very interesting information that deserves further testing using barrels from various companies.

As for the quality of Hart rimfire barrels? One only needs to look at the equipment list from the most recent ARA Indoor Nationals. Fourth, Seventh and Twelveth place were taken, shooting what appears to be the same rifle. Three different competitors using a "Hart" barrel and Eley ammo. Not to shabby!

Congrats to Fred Sears, his daughter and grand daughter on excellent shooting.

All the best, ... John

Hi John:

I must admit I am really suprised that more Hart barrels are not used in BR.

I have had hundreds of barrels in my shop over the years, and the Hart barrels have been by far the most consistent. I honestly have never had one I could not get to meet my base line accuracy criteria. Some took a lot more work that others, but no "duds" of any kind thru the years.

I have certainly seen some as good though - like the first run of the Benchmark 2 groove 18 twist barrels - those were some of the most freakishly accurate barrels I ever worked with!

Thanks for the post,

kev
 
Richard and I was discussing this very thing the other nite,he change the depth of his chamber on a Shilen octogon and it seem to very positive for the MI barrel. Kevin ,maybe depth on certain rifleling has more positive effect than say the 4C or the Ratchet vs say a Octogon, Maybe Richard will post his thoughts on this.

Slick:

I would love to hear them! I was hoping someone else had experimented and could possibly validate my limited testing.

Engraving is a function of bore dimension. The dimension I am referring to is the "C" dimension given on most reamer prints (the distance from the shank face or rim face to the node where the leade begins). The length of the leade is a function of the bore ID.

I have a Schneider Polygon blank in the shot too - that would also make a great test barrel. I would think that, regardless of the configuration, you would not want to push the lead out so far as to have no seal or engagement. I have not tested it, but it makes sense to me that that would be a bad idea?

Thanks,

kev
 
I think you're on the right track Willy. I have a strong suspicion that barrels of different dims and land to groove ratios respond to different chamber configurations. I don't think there is a one size fits all.
- take care - Dave

I wonder if Kevin has tried Eley with these same chambers for a comparison ?

Hi Dave:

No, I have not tried any Eley (even though I still have a ton of it!!).

The folks at Lapua would shoot me if I touched the stuff! (at least I would get shot with some pretty decent ammunition !! LOL)
 
Eley / Lapua use

Hi Gentlemen:

Something else I forgot to mention.

I know most of you use Eley ammunition - I have too (for many years!). In 2007 / 2008 I was testing both (the round nosed bullet and flat nosed EPS bullet) to try to find the best chamber for both. If any of you have tried this, I would really appreciate your experience!

I tested several 5 degree chamber profiles, but found the 2 degree leade (at least for me) the best for both. At .580" it seemed to shoot both bullet profiles well - especially the EPS bullet.

I was wondering if any of you have any experience shooting Eley (SA or the EPS bullet) in a 1.5 degree leade chamber?

Thanks a lot,

kev
 
<SNIP>I would think that, regardless of the configuration, you would not want to push the lead out so far as to have no seal or engagement. I have not tested it, but it makes sense to me that that would be a bad idea?

Thanks,

kev

A couple of days ago I pulled a couple bullets from SK Standard made by Lapua I might add.(lol)

I careful chambered a (bullet-less) round in my rifle with the muzzle pointed up so as not to spill any of the powder. I fired a couple of them this way- the primer fired but the powder was unburnt. I know it takes (back) pressure to get the powder to burn but I figured the primer would be hot enough to ignite the open charge of powder-- but no way.

Next I poured hot wax in the end of the open case on top of the powder to make a seal for a little back pressure- the powder ignited this time.

With the bullet seated off the lands the crimp will supply the necessary back pressure to ignite the powder. I would think with a a little "jam" you now have the crimp and jam supplying the back pressure to ignite the powder.

By adjusting jam are you actually changing "starting" pressure? With the jam set past the second driving band will you have more "launch" pressure that just enguaging the first driving band?

I guess there must be a point of diminishing returns (for a better word) I will use back pressure. I wonder if the crimp allows the powder to reach maxium pressure or if using jam you are adjusting the launch pressure??
 
Polygonal- Octogons-MI

Since these arrive a couple of years ago again ,they have returned with some success,Danny Kenney chambered his own and this starts the 3rd season of it shooting very well indoors, Chris Gilmer and Marc Nachman have two of BC`s rifles that are good also, the lands and grooves are so shallow they hardly engrave a slug in my octogons and they may need a different chamber length to address this. I shoot Eley and the chambers are in the .580 range. Lupua may react well to the longer chamber for the same reason.but there are some Killer 4&5C`s and 4 ratchets that have the .580 . The boys at Rock Creek had their Medford out and it did not seem to take off , The MI Shilen Octogon has some good sucess and with what Richard done lengthening the chamber may be a sign they need different configuration of the chamber to work well .