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Small rifle primer vs large rifle primer. (Read 405 times)

Babydriver Full Member Offline Posts: 155 Joined: Mar 22^nd, 2024	Small rifle primer vs large rifle primer. Sep 24^th, 2025 at 9:14am	Print Post
	I’ve read everything I can about the differences. Does it really make a difference. Even different manufacturers have different dimensions for the same SRP or LRP.


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JHand Full Member Offline Posts: 140 Joined: Apr 15^th, 2024	Re: Small rifle primer vs large rifle primer. Reply #1 - Sep 24^th, 2025 at 9:48am	Print Post
	It is entirely possible my coffee hasn't kicked in yet, but small and large primers have different diameters, so a small will fall out of a large pocket, and a large won't fit in a small pocket. Do you mean large pistol vs large rifle? Those are the same diameter, but slightly different thicknesses


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Statesrights Senior Forum Member Offline Posts: 393 Location: Virginia Joined: May 3^rd, 2016	Re: Small rifle primer vs large rifle primer. Reply #2 - Sep 24^th, 2025 at 10:46am	Print Post
	I have .32-40 brass that takes LR primers and have some that take SR primers. Have not played with the SR brass in some years, but when I did, I didn’t find enough difference (any) to further my efforts with the more exotic brass.


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bpjack Frequent Elocutionist Offline Posts: 3442 Location: East Olympia, WA Joined: May 18^th, 2008	Re: Small rifle primer vs large rifle primer. Reply #3 - Sep 24^th, 2025 at 11:10am	Print Post
	I had the same experience as statesrights. I formed some 32-40 from All American 30-30 brass that has a small rifle primer pocket. I used it for breech seating only as a test when the only primers available were small rifle. Not worth the extra cost. Jack

	ASSRA # 11318 Experience is something you don't get until just after you need it.
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GT Frequent Elocutionist Offline Posts: 2261 Location: Northeast Wyoming Joined: Jun 28^th, 2015	Re: Small rifle primer vs large rifle primer. Reply #4 - Sep 24^th, 2025 at 12:48pm	Print Post
	A suggestion from one of my experiments, if you are so inclined... If you have a couple of cases one with a LRP and one with a SRP, seat a couple of each, minus the powder charge, dim the lights, and pay attention to the exit flame from your barrel. Does it make a difference in your load development? It did in mine. Performance? I don't know as it was significant but it was different. In some loadings a few of us have been known to place paper over the flash hole via one means or another, in some cases this was successful, others not so much. The burn distribution through the paper does have an effect, in my opinion similar to primer size... Here's a couple pics of pet project of mine - I have sleeved a LRP pocket down to a SRP pocket, shot a couple dozen groups in each - as the shooter, I probably got in the way more than I think but even with that assumption, the means didn't justify the ends. Greg

	"To invent, you need a good imagination and a pile of junk" T. A. Edison "The trouble ain't that there is too many fools, but that the lightning ain't distributed right" M.T.
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Bent_Ramrod Frequent Elocutionist Offline Posts: 1536 Location: Southern Arizona Joined: Feb 8^th, 2006	Re: Small rifle primer vs large rifle primer. Reply #5 - Sep 24^th, 2025 at 5:31pm	Print Post
	I tried a couple shots each of .25-20 SS in a Winchester Low Wall, 15 gr RL-7, Ideal 257420 Federal Small Rifle and Remington Large Rifle primers. Average of two shots: SRP: 1977 ft/sec LRP: 2184 ft/sec Tried another experiment with 15gr RL-7/Ideal 257420 50yds 6 shots Fed SRP: 6 in 2-7/8" (5 in 2-1/2") 2004 +/- 32 ft/sec 50yds 6 shots CCI Mag SRP: 6 in 4" (5 in 2-1/4") 2059+/- 102 ft/sec 50yds 7 shots Win LRP: 5-3/8" vertical string; (5 in 3-1/4") 2372+/- 110ft/sec, POI 6" higher than the small primer loads. These were the usual miscellany of cases and the bullets weren't weighed.


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RJ-35-40 Full Member Offline Posts: 195 Joined: Dec 7^th, 2016	Re: Small rifle primer vs large rifle primer. Reply #6 - Nov 9^th, 2025 at 12:47pm	Print Post
	WAY BACK When, I experimented with 45-70 Black Powder Swiss 1 1/2F --- .1" compression Large Pistol primers provided better ES & SD numbers than Lg Rifle Primers. Putting a paper (news print) over the primer helped even more. WAY Back, there was an article in Precision Shooting Magazine (PS) which posited that when shooting black powder, the primer with less brisance (aka force) disturbed the powder column less and therefore provided a more even propagation of the powder ignition. I'm sure drop tubing the powder helps in this regard as well. Taking this further, Way Back when, there was a company that produced bushings to convert a Large Primer pocket to accept small rifle primers. Much like what Greg posted (GT) above. I'm sorry I can't give you any results as to how effective this would be. Maybe a search of this on the PS archives would get you information on the subject. If anyone wanted to go down this rabbit hole and produce these little gems I can dig some out and mail a couple to use as a example to copy. PM me if interested. RJ bpjack wrote on Sep 24^th, 2025 at 11:10am: I had the same experience as statesrights. I formed some 32-40 from All American 30-30 brass that has a small rifle primer pocket. I used it for breech seating only as a test when the only primers available were small rifle. Not worth the extra cost. Jack


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