Large vs small rifle primers and converting large to small

[Varmtr]

G'Day Guys
I may have posted this twice.
Anyway can some one explain to me the benefits of a small primer used in a 308 Palma Lapua size case and I have seen that 6.5 Creed is now coming out in small primer.
I ask this as my 6.5 Epps project in nearly finished and was looking at experimenting to convert large primer pocket to small. I read some time back that it can be done but cant remember on how they did it or if the bushes are still available.
The 6.5 Epps is a 303 Brit neck down and Ackley Improved.
Cheers
Varmtr

 

[J E Custom]

G'Day Guys
I may have posted this twice.
Anyway can some one explain to me the benefits of a small primer used in a 308 Palma Lapua size case and I have seen that 6.5 Creed is now coming out in small primer.
I ask this as my 6.5 Epps project in nearly finished and was looking at experimenting to convert large primer pocket to small. I read some time back that it can be done but cant remember on how they did it or if the bushes are still available.
The 6.5 Epps is a 303 Brit neck down and Ackley Improved.
Cheers
Varmtr

The small rifle primer is slightly more accurate in small bench rest cartridges because of the more concentrated flame front and has a better/more controlled burn. and on small cartridges it appears to have an advantage of .020 to .030 in group size with very little improvement in SDs.

On larger cases there is essentially no measurable difference in group size, but some like to think there is and maybe in there rifles there is enough difference to them to warrant the work to change over. I fired 308s in matches for many years and saw no advantages in this size case, and in cold weather it proved to be a disadvantage to use small rifle primers.

Years ago I experimented with small primes, flash tubes for forward ignition and other changes in primer use to see if these changer were worth the effort. It wasn't in the cartridges I used and changes if the brisance of the primers (Different brands and non magnum primers) proved to have more effect on accuracy. One such case was the use of large rifle primers instead of magnum primers in cases with less than 70 grain powder capacity brought SDs down to single digits.

In cases with 40 grain capacity just changing brands made more accuracy changes than the small primers did.

It is a lot of work to change to small rifle primers unless you can find cases that already have small rifle primer pockets, then it is worth the effort to try and see if they can improve enough to change them.

In Some things, the gain is not worth the pain unless you are looking for any improvements no matter how small.

To satisfy your curiosity you should try them anyway. I made my own bushing that threaded in (32 pitch) to keep from softening the brass and make it stay in the case when de capping. It is also best to reduce the flash hole size at the same time.

At the least, it is an interesting process and worth the effort in knowledge gained. the 303 may be to large for and noticeable change But the fact you are interested is enough to try.

Good Luck and good shooting

J E CUSTOM

 

[Trnelson]

Converting an existing case from a large rifle primer to a small rifle primer would be quite a bit of work. I'm not convinced it would be worth it to even try. Not only is the diameter of the primer smaller, it also requires a smaller flash hole and a more shallow pocket. You either have to fill/add brass material or try to move what is there. Both have issues that would need to be overcome.
Soldering in material would likely soften the case head. You would need to be able to test the hardness and completeness of the fill afterward to ensure it lacked porosity and had sufficient hardness to be safe to use. Then you would need to accurately drill out the pocket and flash hole. Another alternative would be pressing existing pieces in a die to force the material to flow into the space and then repeat the tooling operations to accept the small rifle primer. The problem I see with this option is it would thin out the case head. Making the end product weaker and less tolerant of pressure.
Possibly you could order a large quantity of brass from Bertram or RWS with no primer tooling. This would allow you to tool and finish it to your specification.

 

[Varmtr]

Thanks J E interesting that you threaded the bush it, also how did you reduce the flash hole size.
I tend to think on the same lines that the 303 Brit maybe to big and now its AI'd the case volume has increased even more. But just for ***** n giggles like to give it a try.

Thanks Trnelson yes it would be a bit of work, but you did give me a idea that I never thought of. That was giving Bruce Bertram a call as he is only a 3 and bit hours drive from me, I'll ask if he could make some 303 Brit with small primer and flash. All ready have Bertram 303/25 brass just need to neck up then fire form, or get Bruce to make 303/25 with small flash.

 

[Varmtr]

Well spoke to Bruce Bertram he did say yes it can be done, but is extremely busy trying to keep up with the demand that you guys are ordering.
Also he did say I'm probably the only one asking for 303 Brit with small primer and flash, I would be better off bushing a few cases and experiment with them before putting in an order. The min order was roughly 2000 a bit to many for an experiment that may not work.
Interesting he was doing a run of 6.5-284 with small primer and flash for a customer over your way.

 

[J E Custom]

Thanks J E interesting that you threaded the bush it, also how did you reduce the flash hole size.
I tend to think on the same lines that the 303 Brit maybe to big and now its AI'd the case volume has increased even more. But just for ***** n giggles like to give it a try.

Thanks Trnelson yes it would be a bit of work, but you did give me a idea that I never thought of. That was giving Bruce Bertram a call as he is only a 3 and bit hours drive from me, I'll ask if he could make some 303 Brit with small primer and flash. All ready have Bertram 303/25 brass just need to neck up then fire form, or get Bruce to make 303/25 with small flash.

Threading seemed like the best way to maintain strength and only remove enough for the threads.

I also drilled the existing flash hole slightly and machined a nipple that was a press fit on the threaded bushing so it would be tight when the bushing was threaded in.

using a chamber reamer, I made a collet that perfectly fit the case and used it in my lathe for facing
the bushing, boring the primer pocket and drilling the smaller flash hole. This was to assure concentricity of the primer and flash hole.

It was a fun experiment, but a lot of work. but if it had made a significant improvement, I would have gone to the trouble for my match rifle.

J E CUSTOM

 

[Garycrow]

Trying to fit a bushing or threading in an insert wouldn't help with the biggest advantage of the small primer cases, that is the extra strength and pressure handling abilities. That's the main advantage in my opinion, smaller hole in the cartridge base equals more strength and a bigger safety margin if you like to run stout loads.

 

[Trnelson]

Threading seemed like the best way to maintain strength and only remove enough for the threads.

I also drilled the existing flash hole slightly and machined a nipple that was a press fit on the threaded bushing so it would be tight when the bushing was threaded in.

using a chamber reamer, I made a collet that perfectly fit the case and used it in my lathe for facing
the bushing, boring the primer pocket and drilling the smaller flash hole. This was to assure concentricity of the primer and flash hole.

It was a fun experiment, but a lot of work. but if it had made a significant improvement, I would have gone to the trouble for my match rifle.

J E CUSTOM

Excuse my aside and correct me if I am mistaken, have you not done some experiments on 'forward ignition' and other alternative ignition methods?? A threaded insert would certainly be the preferred method for a large to small primer case conversion. I can't believe I didn't think of that...

 

[J E Custom]

Excuse my aside and correct me if I am mistaken, have you not done some experiments on 'forward ignition' and other alternative ignition methods?? A threaded insert would certainly be the preferred method for a large to small primer case conversion. I can't believe I didn't think of that...

Yes I have tried forward ignition and the primer tubes were also threaded in to the cases. this was a long process and quite time consuming, even though I only did 5 cases to see if there were any advantages.

It appeared that only very large cases need or showed any improvement. (Powder charges larger than 3 or 400 grains.

The reason I wanted to try forward ignition was to see if throat erosion could be minimized by not forcing raw un-burnt powder into the throat. short mags help this condition by shortening the powder column and the flame front, so there was no advantage to forward ignition in my opinion and there was no measurable accuracy improvement.

It was fun and educational to experiment with different ignition methods though.

J E CUSTOM