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

[The Shadow]

You're right on the octagon Willy, the largest pilot of the set for my reamers is almost too small to properly support the reamer on mine. I have a reasonably accurate spring checker. At some point it might be worthwhile to see what the 'holdback' pressure is for different leade angles and chamber lengths. I've got enough barrel segments of most of the barrels used in RFBR to build a test cell. I'm beginning to wonder if by engraving virtually all the bullet using the camming of the action we might actually be reducing the holdback. When I initially slug a barrel the first bit of travel is quite hard but effort is reduced quite rapidly. Maybe by camming the bullet almost it's entire driving length we are doing the heavy lifting instead of the combustion pressure. With lead once it's deformed there is really very little holding pressure as in a jacketed bullet.
- take care- Dave

 

[kevin nevius]

Maybe by camming the bullet almost it's entire driving length we are doing the heavy lifting instead of the combustion pressure. With lead once it's deformed there is really very little holding pressure as in a jacketed bullet.
- take care- Dave

Dave:

I think you are right. It does fly in the face of conventional wisdom though - I had heard a hundred times that more engraving was never a bad thing regarding accuracy.

I have also heard on numerous occasions that once the bullet is initially deformed (passing the leade) the lead - being a "dead" material, remained in that shape. But, there must be some additional deformation taking place for some short length in front of the leade (when the gas pressure is still fairly high)?

I had also thought that the deformation would be much more consistent being seated into a short leade (with lots of engraving) by hand, rather than a long leade where the gas pressure "slams" the bullet thru the leade - but my testing (at least, so far) has not shown it. In both barrels, the accuracy improvement was undeniable.

Thanks,

kev

 

[The Shadow]

Hi Kevin,
I wonder if 'conventional wisdom' predates the new generation of MI barrels ? I don't know anything about those magic Benchmark 2 grooves. Are they relatively wide lands or are they like what we see in a ratchet or 4C ? Just trying to get a handle on the initial resistance the bullet meets in the various barrels.
- take care - Dave

 

[kevin nevius]

Hi Kevin,
I wonder if 'conventional wisdom' predates the new generation of MI barrels ? I don't know anything about those magic Benchmark 2 grooves. Are they relatively wide lands or are they like what we see in a ratchet or 4C ? Just trying to get a handle on the initial resistance the bullet meets in the various barrels.
- take care - Dave

I don't know Dave, has anyone ever defined what criteria a MI barrel must meet?

The BM 2 groove barrels had (have) wide lands - I never measured them though. I will look tonight and let you know.

Rifling depth on a standard Hart barrel is (approx) .0023". Typical "tight" barrels (like those from Lilja) - at least the ones I have measured - mic out at around .2150 x .2200, which would give you rifling depths of about .0025" (comparable to others).

Seems I remember the Benchmarks were very close to the Lilja tight dimensions (I remember they require very small pilots for the reamers!!).

kev

 

[The Shadow]

Kevin,
When you got to your .660 chamber how did it chrono vs the .580 ? If the SD was better it might lend some credence to a kind of damping effect of the extended leade.
- take care - Dave

 

[kevin nevius]

Kevin,
When you got to your .660 chamber how did it chrono vs the .580 ? If the SD was better it might lend some credence to a kind of damping effect of the extended leade.
- take care - Dave

Dave:

My apologies - I never cronographed the initial chambering (if the performance is not acceptable, I typically stop, pull the barrel and rechamber / recrown). I have data on this lot in other barrels (as a baseline) and the data from this chamber in it's current configuration shows a slight improvement from the rest (the ES was 12fps - which is very good in my experience).

Thanks a lot - I have enjoyed our conversation!

kev

 

[The Shadow]

Kevin,
Sounds like you're getting a good start for a run at Perry this year !!!!!! Good luck this year, it's always good to hear of your efforts to expand your knowledge of the sport. If you're like me I tend to learn more from the things I do wrong than the things I do right. Probably strictly a numbers thing !!
- take care - Dave

 

[tim simbari]

Kevin, since there's been a fair bit of commentary about Hart's here I have a question. This has been someting I started to question with Chet Amick before we lost him and it never got pursued. Did you ever measure one with both slugs and pins?

 

[kevin nevius]

Kevin, since there's been a fair bit of commentary about Hart's here I have a question. This has been someting I started to question with Chet Amick beforee we lost him and it never got pursued. Did you ever measure one with both slugs and pins?

Tim:

Yes, I have measured them with both methods.

I have some concerns regarding slugging - I know it is popular (I know BC likes it!). I do it, and it is useful to establish approximate crown locations. I have had many ruined barrels in the shop from people slugging though.

I don't know how Bill does it, but I find the slugs difficult to measure (regardless of the groove counts / locations). Measurement in the ten- thousandths (accurately) is not easy - even if you have the proper equipment. Lead slugs can also deform a tenth with a touch. Maybe it's just me being OCD or meat fisted!! LOL

I wish I had met Chet - he made some really exceptional rifles. David Cramer is using one of his rifles (and beating up on me regularly with it!!). It is a shame we lost him - I would have loved to hear what he had to say about so many topics.

Something else regarding Hart barrrels - most have very little choke in them (one to two tenths in a 24" blank is common). I absolutely believe choke is important (especially at the crown location), but more choke is not necessarily better. These barrels shoot very well with very little.

Thanks for the post, have a great weekend!

kev

 

[Big_G]

Chambers

Kevin there is an article on 6mmbenchrest.com about how Bill Myers chambers his rifles. Its at the bottom of the article on Joe Fredrick. You can google it under >>>Bill Myers gunsmith. According to the article Mr. Myers just barely engraves the bullet.
Dan

 

[tim simbari]

Tim:

Yes, I have measured them with both methods.

I have some concerns regarding slugging - I know it is popular (I know BC likes it!). I do it, and it is useful to establish approximate crown locations. I have had many ruined barrels in the shop from people slugging though.

I don't know how Bill does it, but I find the slugs difficult to measure (regardless of the groove counts / locations). Measurement in the ten- thousandths (accurately) is not easy - even if you have the proper equipment. Lead slugs can also deform a tenth with a touch. Maybe it's just me being OCD or meat fisted!! LOL

I wish I had met Chet - he made some really exceptional rifles. David Cramer is using one of his rifles (and beating up on me regularly with it!!). It is a shame we lost him - I would have loved to hear what he had to say about so many topics.

Something else regarding Hart barrrels - most have very little choke in them (one to two tenths in a 24" blank is common). I absolutely believe choke is important (especially at the crown location), but more choke is not necessarily better. These barrels shoot very well with very little.

Thanks for the post, have a great weekend!

kev

Thanks, but that's not where I'm going with this nor why I posed the question. Now going back to Chet, he was the first guy I knew that invested a fortune in a set of pins from .2140 up to .2180 right down to 1/2 tenths...cost a fortune. Anyway he did this because everything he did was driven by bore diameter not groove, he felt bore diameter drove how good and how soon a bore sealed. He was of the opinion that without good and fast sealing everything else was compromised. About this time I was getting decent at slugging and able to measure reasonably well. Anyway there were a couple barrels from Hart that I measured up, slugged them and at that time they were running somewhat larger but slugs showed between 1-2 tenths no surprise. Chet dropped pins down them and time and again he calls me....no taper. I get them back, clean, lube, slug, 1-2 tenths taper....why? Everything I ever learned about barrel lapping always indicated almost the same metal removed both bore and groove, maybe a bit more in the groove diameter but this was a mystery and not unique to 1 or 2 barrels. The question remains why? and how significant to their performance??

Any thoughts?

 

[ivanhoe1222]

Lapping, just a thought

If you borescope a barrel before and after it has been lapped you can see a small amount of taper on the grove area. I think this is from the torqueing of the lap as it is being pushed through the twist of the barrel (rifle twist 1-16 1-16.5 and so on). I do not have a way to measure this unless I destroy the barrel in the process. I also think this is a free added benefit, helping in the sealing process of the bullet as it passes the length of the barrel. Just a thought.
Ivanhoe

 

[Keyhole]

Benchmark

Kevin,
Thanks for posting! I just recieved a Benchmark 1/16.5 three grove . When I ordered I did not know about the MI. Is this an option?
I am planning on setting this barrel up for Lapua Center X . I shot this ammo in my Hart barrel scope rifle at River Bends last two metric matches,WOW ! It shot well.
Howard

 

[tim simbari]

If you borescope a barrel before and after it has been lapped you can see a small amount of taper on the grove area. I think this is from the torqueing of the lap as it is being pushed through the twist of the barrel (rifle twist 1-16 1-16.5 and so on). I do not have a way to measure this unless I destroy the barrel in the process. I also think this is a free added benefit, helping in the sealing process of the bullet as it passes the length of the barrel. Just a thought.
Ivanhoe

There is no torqueing of a lap running through the barrel, the lands are same dimension from one end to the other in quality match SS barrels.

 

[kevin nevius]

Anyway there were a couple barrels from Hart that I measured up, slugged them and at that time they were running somewhat larger but slugs showed between 1-2 tenths no surprise. Chet dropped pins down them and time and again he calls me....no taper. I get them back, clean, lube, slug, 1-2 tenths taper....why? Everything I ever learned about barrel lapping always indicated almost the same metal removed both bore and groove, maybe a bit more in the groove diameter but this was a mystery and not unique to 1 or 2 barrels. The question remains why? and how significant to their performance??

Any thoughts?

Tim:

My apologies - I do get to rambling sometimes!!

I wish I could answer your question - my pins are in two tenths increments, and I have never conducted the test you mentioned.

Personally (another ramble coming on!) I think way too much emphasis has been placed on the importance of slugging. IMHO it is useful for verifying choke and crown placement, but that's all.

You simply cannot predetermine a barrels true performance without shooting it.

Choke amount is also a fairly useless number - I have three Anschutz factory take off barrels that have six tenths (plus!) of choke and have never been competitive.

One of the test barrels I mentioned in this thread (the three groove Hart) has no measurable choke - I can't feel it either when I slug it - but it is a great barrel, and I am very hopeful so far.

Sorry I can't help with your question, thanks for the reply!

kev

 

[kevin nevius]

Tim:

Do you know if Chet lapped his barrels?

If he did,did he lap them all or just some of them?

Would you know what his criteria was for lapping them (was it performance based, after he tested them)?

Thanks,

kev

 

[tim simbari]

Tim:

Do you know if Chet lapped his barrels?

If he did,did he lap them all or just some of them?

Would you know what his criteria was for lapping them (was it performance based, after he tested them)?

Thanks,

kev

Yep I do. He lapped every single one and I'll throw you a little curve ball on that in a bit.
He was of the opinion, at the end, that barrels [in his estimation] should not be much over .217, he liked them .2168 .2169 with 2-3 tenths of taper. He would if necessary lap his own taper in but if given an ideal choice wanted only to put a finish lap in. He would also have a barrel off and back on several times playing with slight lap variations. The guy was fanatical about getting them as good as the metal would allow.
He was doing some barrels where he did the entire lap from a maker he would never identify. These were used, if I'm not mistaken for USA biathalon members.
The thing I found quite surprising was that his final lap was 1000 grit and was using a very unique compound unavailable through commercial sources, he secured a good supply from NASA. He swore that finish with those dimensions resulted in a slug that got very quiet very early in the bore.
He shot everything. As a mater of fact, even with the few customers he would do work with he would not part with a gun until tuned and you needed to send him a good couple bricks to tune.
The othe interesting part of his barrel work was that he did lots of them on Ans 54's and Suhl's and rarely threaded them, developed a decent press. He was of the opinion that the German's knew plenty about threading and refrained intentially, because they/he felt pressing yielded a more uniform, stress free chamber.
Lastly he did everything with a SINGLE reamer that was "never leaving his hands" and I don't know what became of it. He also spent a lot of time on cutting fluid development and would not say much about it other than "mostly natural" and I believe one reference to lard oil based.

 

[Que]

now this is a dang good thread. thanks for the info gents

 

[The Shadow]

Hi Kevin,
Hope you had a good weekend. I've been thinking about your Hart's. What finished length do you prefer ? I know you said your barrels have only a slight amount of choke. Have you ever had one that worked well in the cold with a greater amount of choke ? I have a barrel that I think needs some additional lapping in the choke area as it tends to feel crusty the first patch through, like the wax isn't being carried all the way down the tube once the temps drop. It seems to start just after the constriction. This barrel is just at 26". Does Hart consciously put a choke in their barrels or are they just lightly taper lapped - which I think is the correct way.
- take care - Dave

 

[kevin nevius]

Hi Kevin,
Hope you had a good weekend. I've been thinking about your Hart's. What finished length do you prefer ? I know you said your barrels have only a slight amount of choke. Have you ever had one that worked well in the cold with a greater amount of choke ? I have a barrel that I think needs some additional lapping in the choke area as it tends to feel crusty the first patch through, like the wax isn't being carried all the way down the tube once the temps drop. It seems to start just after the constriction. This barrel is just at 26". Does Hart consciously put a choke in their barrels or are they just lightly taper lapped - which I think is the correct way.
- take care - Dave

Dave:

Hope you had a great weekend too (getting ready for Christmas here!)

I have come to like a certain balance in my rifles thru the years - I can't shoot a muzzle heavy rifle deep into the strings (hurts too bad as I get older!). I have settled on a contour that gets me the sight radius I need, and keeps some of the weight down.

I typically order blanks in the 26" finish range. I evaluate them, and do an initial fitting / testing. If I don't see some promise, I remove and set back the crown .060" at a time until I see something from them. Small movements in crown placement produce (sometimes) dramatic results. All of the testing is done with anextension tube / tuner. I begin the fine tuning after this initial fitting is concluded.

Most finish near 24" (to make a short answer very long!! LOL).

Harts (to the best of my knowledge) are all taper lapped. My favorites are the 17 twists (in either 3 or 6 groove). The 17 seems to perform better at 100yards, especially in some wind - which we always see!

Taper amount (or choke amount) seem to have little bearing on performance. I have tested barrels with large amounts of each, some shot very well, some not. You just can't tell what you have (after everything is done right) until you shoot it. I do know that some (however small) must be there though, and as BC has stated the crown placement must be at the tightest (and roundest) spot.

I am sorry I cannot comment - I do very litttle cold weather SB shooting or testing. This year was an exception (because of the tremendous amount of rain we have had), I was still testing as late as two weeks ago. I hope the cold weather results translate to great summer performance.

THanks for the reply,

kev