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Babydriver
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Small rifle primer vs large rifle primer.
Sep 24th, 2025 at 9:14am
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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
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Re: Small rifle primer vs large rifle primer.
Reply #1 - Sep 24th, 2025 at 9:48am
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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
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Re: Small rifle primer vs large rifle primer.
Reply #2 - Sep 24th, 2025 at 10:46am
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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
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Re: Small rifle primer vs large rifle primer.
Reply #3 - Sep 24th, 2025 at 11:10am
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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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GT
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Re: Small rifle primer vs large rifle primer.
Reply #4 - Sep 24th, 2025 at 12:48pm
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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
  

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Bent_Ramrod
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Re: Small rifle primer vs large rifle primer.
Reply #5 - Sep 24th, 2025 at 5:31pm
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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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