Rimfire chamber specs

[SteveOak]

Has anyone developed a formula or set of specs such as reamer dimensions, head space, rim depth etc for a specific brand of rimfire ammo?

It is pretty common that you buy a rifle or have one built or rebarreled and then go through a process of determining which flavor of ammo, Eley or Lapua being the major players, give the best results.

Seems that there would be something other than Voodoo or happenstance that causes one particular brand to perform well and the other to perform not as well or not well at all.

If it is a function of dimensions then it would follow that the dimensions, could be divided into three major categories.

1. Shoots both to an acceptable level but prefers Eley

2. Shoots both to an acceptable level but prefers Lapua

3. Shoots one or the other quite well but shoots the other very poorly.

It would seem that both 1 and 2 are less then preferable outcomes and that 3 is much preferred unless of course your rifle now prefers the ‘wrong’ ammo. LOL

It would seem that 3 is the preferred outcome as it would indicate a strong optimization of dimensions for a particular brand while both 1 and 2 could probably perform better than they do if the rifle had a stronger preference for one brand.

I am exploring this as I am getting ready to have a rifle built and will need to spec a chamber. I would prefer to steer the results for the best outcome rather than throw a couple of thousand dollars at a rifle and cross my fingers that I will get a rifle that shoots well.

The dimension that I am looking at as the most important dimension is the profile of the bullet. A rounder bullet would probably like a steeper leade angle then the headspace would be the secondary dimension, both being critical.

I have not explored rimfire chambering dimensions enough to know if there are more to be considered. If anyone can post a drawing with comprehensive chamber dimensions I would appreciate it.

 

[patriot]

How would you know what bore size, barrel length & profile, land/grove configuration & dimensions, type of steel, muzzle choke... would be optimal for a Lapua or Eley specific chamber?

Mark

 

[SteveOak]

Please provide whatever information you have to support the conclusion that any of those factors would cause a rifle to favor or disfavor Eley or Lapua rimfire ammo. That would be a valuable and appreciated contribution.

Data would of course be best. Anecdotal information may also be of value. "I think," not so much.

It is likely that a list of characteristics can be developed, sorted into those that do and those that do not have an affect and further sorted into those that have a major effect (or are essential) and those that have a lesser effect.

 

[patriot]

If I had that information I would have made a statement rather than ask a question; wish I did. My point was you are not evaluating the entire system. It might be best to copy what has proven successful; perhaps speak with Dan Lilja or another of the barrel manufactures. As far as I know the empirical data doesn't exist; just theories. But I'm researching an approach to measuring the relationships.

Mark

 

[bugman]

You should consider asking these questions at www.rimfireaccuracy.com

Joining that site will also give you access to searching previous posts from members that have done a lot of testing for the data you seek...I will not post names here, but you can PM me for some. Be prepared for many variables, like leade length, engraving, case taper, etc. that you may or may not have considered.

There will be no easy and all-inclusive answer for you. Generally, eley (tenex and match) works best with reamers with specific dimensions. Generally, the growing movement toward other ammo brands (Lapua, RWS, etc) has resulted in reamers with slightly different dimensions. Straight-line empirical evidence does not exist, and having to test specific lots of your chosen brand of ammo is still a necessity after you get your chamber speced

Since you state you are going to build a rifle, contact one of the top RIMFIRE smiths and ask for some advise/opinions. Richard Gorham comes to mind, but there are others.

FWIW, if I had to do this again, I would contact a winning RIMFIRE smith and get his input and current advise on chambering /ammo.. Then, I would decide on the brand of ammo I was going to shoot....tell the smith your choice of ammo brand, and then follow his recommendations for the rest of the components for the build.

Based on your OP, I am assuming you are going to get into serious bench rest components. If that is the case, chamber dimensions is only the tip of the iceberg in this situation.

Jack

 

[centershot]

I had a gunsmith friend who experimented with different lead angles at the front of the chamber. Made quite a difference. Unfortunately, he is deceased. Just an fyi, I had a rim thickness gauge which I quit using in favor of weighing the rounds.

 

[bugman]

I had a gunsmith friend who experimented with different lead angles at the front of the chamber. Made quite a difference. Unfortunately, he is deceased. Just an fyi, I had a rim thickness gauge which I quit using in favor of weighing the rounds.

I agree... the leade angle (and leade length/amount of engraving) will make a difference.

I think a lot of us have gone thru the sorting via rim thickness/headspace, weight, and, now, engraving length of marks on the bullet. IMO, I am not convinced any of it makes much difference if you are shooting QUALITY ammo. Lately, I spend my energy finding a lot that gives good results on paper. And I find that culling that lot of ammo makes very little difference in scores.

You should keep doing what you have confidence in. IOW, if it works for you, don't stop doing it because of my opinion. Confidence in your equipment and ammo is half the battle in rim fire.

Jack

 

[Tim s]

Has anyone developed a formula or set of specs such as reamer dimensions, head space, rim depth etc for a specific brand of rimfire ammo?

It is pretty common that you buy a rifle or have one built or rebarreled and then go through a process of determining which flavor of ammo, Eley or Lapua being the major players, give the best results.

Seems that there would be something other than Voodoo or happenstance that causes one particular brand to perform well and the other to perform not as well or not well at all.

If it is a function of dimensions then the results then the results and it would follow, the dimensions, could be divided into three major categories.

1. Shoots both to an acceptable level but prefers Eley

2. Shoots both to an acceptable level but prefers Lapua

3. Shoots one or the other quite well but shoots the other very poorly.

It would seem that both 1 and 2 are less then preferable outcomes and that 3 is much preferred unless of course your rifle now prefers the ‘wrong’ ammo. LOL

It would seem that 3 is the preferred outcome as it would indicate a strong optimization of dimensions for a particular brand while both 1 and 2 could probably perform better than they do if the rifle had a stronger preference for one brand.

I am exploring this as I am getting ready to have a rifle built and will need to spec a chamber. I would prefer to steer the results for the best outcome rather than throw a couple of thousand dollars at a rifle and cross my fingers that I will get a rifle that shoots well.

The dimension that I am looking at as the most important dimension is the profile of the bullet. A rounder bullet would probably like a steeper leade angle then the headspace as being the secondary dimension, both being critical.

I have not explored rimfire chambering dimensions enough to know if there are more to be considered. If anyone can post a drawing with comprehensive chamber dimensions I would appreciate it.

Would it not be a good idea to have this conversation with the smith doing the work?
If it's a BR gun, well over 90% of them are setup primarily for ELEY, the biggest variable being the leade angle, generally from 1deg to 3 deg.
Most guns set up like this will be OK with Lapua or RWS if you find a consistant
lot.

 

[SteveOak]

I haven't picked a gunsmith yet. I am looking to educate myself in advance.

Most people couldn't be bothered exploring how this might work. I consider it fun.

It seems to me that if certain chamber dimensions produce a rifle that shoots Eley well and still shoots Lapua ok perhaps further optimization is possible resulting in the rifle shooting Eley even better. That is the purpose of this exercise, to identify the optimum chamber characteristics to produce a chamber that most strongly prefers one brand of ammo. Pretty much along the path that bugman has stated but starting with solicitation of information from a much larger source, that being the collective wisdom and experience of the 'accurate shooters' that participate in this forum.

The keystone seems to be the bullet shape with Eley and Lapua having a different bullet shape and it would follow, perform best with a different leade angle.

Does anyone have any information to support or refute that assumption?

 

[Outrider27]

Since you are obviously serious about this and serious about gathering appropriate knowledge, I would suggest that you start by buying, begging, borrowing or stealing a copy of "The Art of Rimfire Accuracy" by Bill Calfee. Of particular interest and use to you will be the chapter entitled "How To Do Rimfire Benchrest Part 1, The Barrel", and the chapter entitled "The Good The Bad And The Ugly" - this latter chapter discusses leade angle in detail, as well as chamber body shape. The chapters with discussions concerning barrel contouring and lapping (including what order they should be done in a rimfire barrel blank) and which end should be chambered (regardless of what the barrel maker marks as the breech) will also be instructive - at least I found them so - as will the discussions on tuners.

Have a good time with this project; it sounds like it will be a fun ride for you.

Mike

 

[aloreman]

Wouldnt it be easier to just use a tuner?

 

[SteveOak]

A tuner does not deal with the same aspects as will a proper chamber.

Easy is not one of the decision criterion.

 

[Shynloco]

A tuner does not deal with the same aspects as will a proper chamber.

Easy is not one of the decision criterion.

Steve,
I'm curious about the comments you've made. Perhaps I've misunderstood what you've written, but are you "suggesting" that you want to have a rifle built that will "perform" best using a specific type/brand of Rimfire Ammunition (i.e.Lapua (ie. CenterX, Midas+ etc). Eley (Tenex, Black) Federal Ultra Match UM22 or any of the other "Match Ammos"? If that is in fact what you are doing, that pretty much defies any of the "accepted" and "proven" methods of finding the most accurate ammunition made that performs the best in your particular rifle. And there are reasons for that which include.... it is a well established fact that Rimfire rifles are most sensitive in terms of the ammo they are fed. You can buy two high quality Rimfire Rifles of the same make and model (say an Anschutz 2013, etc and even consecutive serial numbers, and there is no guarantee they will like or shoot the same brand of ammo as accurately as the other. The second consideration is that many serious competitors are "lot minded" which means they search for a specific lot that works the best in their rifle and then buy a case or two because even with same brands of Rimfire Ammo, a lot change CAN have a dramatic impact upon the performance in a specific rifle, with or without a tuner. And BTW, a tuner can ONLY improve upon a specific ammo's performance once that ammo has been established to shoot the most accurately in a specific rifle.

Lastly, might I suggest you get hold of a book entitled, "Rifleman's Guide to Rimfire Ammunition" written by Steve Boelter. Steve does show up on Rimfire Central now and then and is not only only a builder of Olympic (US Olympic Team) quality Rimfire Rifles, but can answer any questions related to reamers, leads, headspace, custom reamers and anything else used to build a seriously competitive Rimfire Rifle. And you can bet that such a rifle will cost as much as (or even more say around $7-$10,000 without glass) any custom built centerfire rifle you can have built by any of the top builders of centerfire rifles whose names appear on a list of well established Gunsmiths in the opening pages of this blog. And for whatever its worth, finding a Gunsmith willing to build you that RIMFIRE rifle is no easy task and the wait time can be more than a year. Thx.

Alex

 

[rayjay]

The shape of the nose of the bullet doesn't affect the shape of the driving band of the bullet. The driving band is where the bullet is engraved by the rifling.

My range's RFBR match uses a dual yardage format with targets shot at both 50 and 100 yards. We have been doing this for about 4 years now and the one thing I have seen without fail is that Eley Team, Match or Tenex outperforms Lapua CenterX at 100 yards. At 50 yards the CX will shoot well and was used to shoot the first 250 at 50 in our matches [ no national level shooters here ]. But at 100 yds the top score is always shot with Eley. The 100 yd target has a 1" ten ring that you shoot 5 shots at [ IBS 200 yd CF score target ]. We use the RBA target at 50.

 

[patriot]

The smallbore prone national champion shoots Lapua.

 

[rayjay]

The smallbore prone national champion shoots Lapua.

Center X ?

 

[SteveOak]

Hello Alex and to all,

I hope that you are well.

Alex, you have it exactly correct. I am researching the parameters that cause a rifle to shoot one particular brand of ammo, be it Eley or Lapua, better than the other.

My hypothesis is that there must be a cause that is related to the physical attributes of the rifle. Perhaps the 'tried and true' method of chambering a rifle leaves something on the table. If we can identify those physical attributes then we can spec a rifle that is better optimized and have an even stronger preference for that brand and hopefully shoot it even better than a lesser optimized rifle.

I would then proceed to sample different lots to further refine the selection. My expectation is the the lot to lot variance of the bullet shape, and other characteristics are small compared to the difference from brand to brand.

The shape of the nose of the bullet doesn't affect the shape of the driving band of the bullet. The driving band is where the bullet is engraved by the rifling.

Exactly the kind of info I am looking for, thanks!

The smallbore prone national champion shoots Lapua.

Interesting!

 

[rayjay]

Due to a variety of circumstances I only got to shoot in 2 of my club's RFBR matches last year. I shot a different rifle in each match. I shot different ammo in each match. Neither rifle had ever shot the ammo I used.

In both cases as I was shooting the sighters for the first relay [ which is 100 yds ] I thought "WHOAA!!!! I'm wasting my time with sighters, I need to be shooting records!!". In the first match [ June ] I was shooting a Walther KK200 that is in a current state of the art BR stock. I had some Eley Team that I had just about wrote off and no good for anything but pulling the bullets for slugging. I decided just to take it and shoot it up. WOW did that ammo work in that gun on that day in those diabolically bad wind conditions. The scores were nothing to write home about but good enough to win. The 2 points I won by at 100 sealed the deal.

In July I took a Hall with an experimental bbl. It's a sporter reverse taper with the dog knot turned off and a Fudd tuner installed. I took some Eley Match EPS that was actually bought for another [ now apart ] rifle. I decided what the heck. Same deal as June. First few sighters "WHOOA!!". The conditions were the best I've ever seen at this range. I fired my first 250 !!!! WOOTT !! Also did ok at 50, good enough to win although I did give away a point or 2. This bbl set up has a ton of vertical with wind shifts but very little horizontal. Figuring this stuff out in a match is definitely not the ideal

Who knows what these rifles might do with this ammo with some tuner twisting. In both instances the tuner was just stuck on and the shooting begun.

IMO, this shows the importance of lot testing.

 

[SteveOak]

Does anyone have precision drawings of Eley and Lapua rimfire cartridges and also bullets.

 

[Tim s]

I haven't picked a gunsmith yet. I am looking to educate myself in advance.

Most people couldn't be bothered exploring how this might work. I consider it fun.

It seems to me that if certain chamber dimensions produce a rifle that shoots Eley well and still shoots Lapua ok perhaps further optimization is possible resulting in the rifle shooting Eley even better. That is the purpose of this exercise, to identify the optimum chamber characteristics to produce a chamber that most strongly prefers one brand of ammo. Pretty much along the path that bugman has stated but starting with solicitation of information from a much larger source, that being the collective wisdom and experience of the 'accurate shooters' that participate in this forum.

The keystone seems to be the bullet shape with Eley and Lapua having a different bullet shape and it would follow, perform best with a different leade angle.

Does anyone have any information to support or refute that assumption?

You're assumtions are, in fact, wrong as well as your shape theory. It boils down , more, to OAL than anything you've mentioned, as well as certain chambers work far better with certain barrel configurations.
Most accomplished smiths dread dealing with a customer with heavy pre concieved notions.
Getting answers is Ok. Asking the right questions is more important.
Several guys will tell you what chamber works best without a definative answer as to why.