Do Primers Affect Group Size?

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John Alexander posted this 29 October 2022

I'm sure that primers make a difference when inappropiate primers are used such when regular primers are used when mag primers are needed to ignite heavily coated slow burning powder.

My question is do different brand primers affect group size when used with fast or medium burning rate powders and at the velocities of normal cast bullet velocities.

I have always been agnostic (promiscuous may be a better word) about primer selection using whatever was handy. It seemed to me that if they went bang they were all the same. I once tried the Federal 205M primers used by 99.9% of jb bench resters but couldn't see any improvement. I recently used some of these in a load and rifle that I have good records on.  Nine 5-shot groups with 205M averaged substantially worse than usual with this load.  I am skeptical but will try to repeat and see what happens.

Anecdotal evidence abounds about one primer or another causing either better or worse groups, but have there been any serious tests that have found repeatable differences in accuracy with different primer brands?

John

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Ross Smith posted this 29 October 2022

The only difference that I've noticed-not tested- was with magnum primers used to get compressed loads og FFg burning. Did very well.

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Little Debbie posted this 29 October 2022

Yes they do make a difference in accuracy in cast bullet loads using medium and fast powders.  I shot an exstendive test in my 6mm PPC with cast bullets comparing pistol and rifle primers.  The rifle primers shot measurably better with that load /,bullet combo.  I’ve seen this phenomenon on the target (not anecdotal) in many situations, primer type, brand, and lot makes an accuracy difference.
The current supply situation it’s tougher to get a variety of primers to test for best accuracy.  My current testing is to determine which loads I can substitute pistol primers for rifle. This is because I have more pistol primers than rifle.

 

My current rule of thumb is this:

Pistol primers work fine with pistol and shotgun type powders in rifle loads. When fine powders migrate into the flash hole you get vertical stringing. Store the rounds bullet  down and give a light tap on the round with the bullet down prevents this.

Rifle primers are best with rifle type powders 4198,4759, 4277, 4895 etc even in “light” cast loads.

 

I’m still trying to get groups consistently under MOA with cast bullets.  Trying different primers is a variable I always try in load development.

 

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Wm Cook posted this 29 October 2022

John asked “ will different brand primers affect group size when used with fast or medium burning rate powders and at the velocities of normal cast bullet velocities.”

That sets a very specific range of variables with the wild card being the powder charge may need to be tuned to the primer. So I’ll avoid that one.

John can confirm this or not but taken at its lowest common denominator I think he’s asking (might be wrong, frequently am) that assuming you have a bread and butter cartridge like the .308 and you have a load developed that gives you a round evenly distributed 1 1/2” group using CCI, will the group suffer or improve if all variables are kept the same but the loader substitutes the CCI with Win, Fed, or Remington primers.

The biggest nut to crack is when you stretch the expectations such that you have two proven loads with the same rifle; one with fast and one with medium burning rate. And then do the primer comparison.

The thought of that gives me a headache. Great thread! Bill C.

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Qc Pistolero posted this 30 October 2022

I started asking questions when I was having problems with my 30-30 in competition having vertical stringing when the temp would go down at or below freezing point.Ed Harris suggested I'd use mag primers and it did help a lot.

I started using regular LR primers during summertime and mag primers when it was getting cold;my scores improved due to less vertical stringing(guess I should send a few $bills to Mr Harris).

Mag primers definitely have an hotter spark and should be taken into account not only for the type of powder they're being used with but also at what temperature they are going to be used.As far as I'm concerned,40*F is about when I switch to mag primers whatever the powder I'm using.

LP primers having a cup slightly lower than LR primers are not,according to my tests as accurate as LR primers.Besides having a lower temp spark,I think that some of the force of the firing pin is absorbed by the 2/1000'' shorter cup being driven to fully seat in the pocket.It always translated for me in that old buggaboo vertical stringing.

 

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RicinYakima posted this 30 October 2022

I shoot two early Stevens firearms; an 1865 rifle in 35 Stevens and a 32 Short pistol converted to CF. Both require Federal standard primers because the firing pin strike is so light. And Federal has the softest and thinnest cups. Both were made to shoot pure copper primer cups.  FWIW

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comprschrg posted this 30 October 2022

This is interesting to me. I'm not trying to be facetious. But initially I learned magnum primers had more heat/fire/umpf. Then through much reading , was informed only the cups were thicker to withstand more pressure.
Now ......back to magnum primers have more spark. As it may. Just today I was reading a different make was only the difference in say 1/2 grain of powder in load development. I am only a neophyte in this art, so please understand I'm trying to learn.

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Bud Hyett posted this 30 October 2022

Thought One: Based on experimenting a half-century ago, you can find a difference in primers. You might wear a barrel out getting there. 

I had only two centerfire rifles, a 788 .222 Remington and a 700 BDL .270 Winchester. Both shot sub-minute ten-shot groups. The .222 with Sierra 53 grain Match and the .270 with Sierra 90 Hollowpoint. Remington  standard primers in both rifles. Then I was given a carton of W-W 8 1/2 primers (wooden trays) to use.

I substituted these primers and the rifle did not shoot as well. The groups were minute and one-half and not going down, interesting. I raised and lowered the powder charge, no help. Then I moved to powder one burning rate slower and one powder rate slower raising and lowering the powder charge. Then I moved to powder two burning rates slower and two powder rates slower raising and lowering the powder charge.

Eventually I found a load shooting near the original. But I'd put over 500 test rounds through the barrel in the journey. 

Thought Two:

Primers (design philosophy):

  • Federal and Winchester are designed to throw the flame forward and ignite the powder column from the center outward.
  • CCI is designed to throw the flame outward at the back of the powder column to ignite the powder column to burn progressively forward to the front.
  • Remington throw the flame in a 45-degree angle to ignite the center and burn both outward and forward.
  • With the shorter, fatter, sharp-shouldered cases in use today, the CCI primer is gaining more usage.
  • I find when switching there is a load with a slightly faster or slightly slower powder that will shoot consistently as the first load.
  • Therefore, I standardize on a primer for a load and work forward. 
  • Federal or Winchester for long cases (.e.g., 30-'06), Remington or CCI for shorter cases (e.g., 6mm BR)

 

Farm boy from Illinois, living in the magical Pacific Northwest

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M1fuzz posted this 30 October 2022

Now this isn’t scientific by any means but, over the years I have found that if everything is the same in a cast load in my military bolt action rifles by using Winchester Large Rifle Primers will always tighten up the group not by much but, you can tell the difference.

Now, using a CCI 34 primer makes the groups smaller in one of my M1 Garands I use for cast. I have made a repro early to mid 60’s M16/AR15. That rifle seems to group the tightest using CCI 41’s.

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Fitzpatrick posted this 30 October 2022

Over the last couple of years I have been forced to try different primers in different calibers . I have come to the conclusion that if I work up the load you can achieve the same group size with in reason , I did have some hang fires in 308 based wildcats that I tried small primers in but even then using pistol powder solved most of that. Of course accuracy is in the eye of the beholder , if I can get a load to group at around a inch at a 100 yrds  that is a good hunting round . But in the end I think if loads are developed with a primer that you have on hand you can achieve acceptable results , with the exception of bench rest competition . and all my testing reloaded primers was also used with the same accuracy 1 moa  and continued shooting and enjoyment thou this time of no components

 

  just my two cents  James

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comprschrg posted this 30 October 2022

Thank you Bud. And M1fuzz. I'll be copying those posts to my notebook, then going back to the side line.

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Rich/WIS posted this 30 October 2022

Not an opinion on accuracy (me and my rifles are not good enougn to tell) but did notice that had occasional delays in ignition with ballpowders and standard primers.  I use magnum primers with Ball C2 and Win 748, standard with others.  Noticed the delay when shooting with electronic ear muffs, most went bang when the firing pin hit but a few there were a few where you heard a click-bang.

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JeffinNZ posted this 30 October 2022

Depends.  

My Hornet is fussy with primers depending on powder.  Stick powder not so much.  Ball powder, will only shoot with Winchester primers presumably as they are hotter.

I tend to think small cartridges can be picky about primers.  Large cartridges, no.

Cheers from New Zealand

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Wineman posted this 30 October 2022

I have shot 308 Win in an Ishapore 2A1 using Winchester LP primers, a 312299 and 15.5 grains of Alliant 2400. First shot pierced the primer, stopped there and broke that ammo down. Accuracy was good, but hard on the gun.

Dave

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Tom Acheson posted this 31 October 2022

For my CBA benchrest match guns, I’ve been using small rifle BR primers since 2005. Accuracy testing each time I changed to a different chambering, had me using R-P 7 ½ or FC 205M primers, depending on the chambering. For my revolver loads using large primers, I’ve found most brands do OK. Interesting that there are now some 45 ACP cases that use small pistol primers.

 

However, for my black powder cartridge loads, I’ve seen a trend of accuracy improvement where FC 150 (large pistol) match primers, along with a disc of wax paper dropped into the case before the powder goes in, is working well. Supposedly the wax paper softens, diffuses or spreads the primer “flame” to optimize ignition. Other shooter’s have commented that the shorter pistol primers (in the primer pocket) contribute to peening of the face of the breech block. In doing this for the past 5-years, I see no evidence of that in my rifle. It’s a C Sharps Model 74 chambered in 40 cal. 2 ½.

 

Tom

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Hornet posted this 31 October 2022

Do different brand primers affect group size when used with fast or medium burning rate powders and at the velocities of normal cast bullet velocities?  Yes.

Oh, you want a little detail? Picky, picky.. Example: Remington 799, .22 K-Hornet, 1:12" twist, NOE 225-60-RN, 17 BHN, 59.5 +/- 0.1grain,  fireformed WW Cases, 5 shot groups,  AA1680 powder 9.3,9.5,9.7,9.9,10.1grains, WSR vs WSP, alternating groups between primers.   Result: groups using WSR were more rounded and visibly averaging smaller than the WSP groups. Repeated a few days later using WSR vs R-P 7-1/2, same powders charges. Result: R-P 7-1/2 groups clearly better than WSR groups. Annoyingly enough, the R-P 7-1/2 primers used were the old copper-washed version. I ran out and changed to the current brass-finish ones and groups got significantly worse, back to matching the WSR. Really need to retry with R-P vs Fed 205M some day.

Similar testing with the RCBS 22-055-FN (Cramer hollow-pointed version) showed a similar pattern with IMR 4227 in doses of 9.8, 10.0, 10.2, and 10.4 grains and those used R-P 7-1/2, WSR and Fed 205M with the Fed 205M clearly best. Disappointing since the .222 and .223 also prefer the Fed 205M in similar testing in loads around 2100 fps with SR4759 and use large quantities of them. I may need to try a faster powder for the R-P's to work (got lots of them).

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RicinYakima posted this 01 November 2022

I'll ask this question; I have lots of small rifle primers and less than 100 small pistol primers and none available locally. I want to load some cast bullets in my Savage 22 Hornet. I have lots of 225438s cast and and looking for a light load I can use with SR primers. Any help out there?

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Wm Cook posted this 5 weeks ago

Rick here's some numbers that I just pulled off my computer this week.  I was hoping to get out once more this year to give these loads a try. So I was getting my ducks in a row for the next range trip.  All 5 shot 100 yards, mixed Fed and Rem SR. Wasn't smart enough then to shoot 10, 20 shot groups..

So I thought these were the best of the powders and loads to look at again.  I also tried Lil Gun, 2400, 5744 and W231 and they didn't shoot as well.  Some of those groups were real ugly  Some over 10".  But I was shooting velocities from 700 to maybe 1300 fps.  Bill C

 

 

 

 

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RicinYakima posted this 5 weeks ago

Thanks Bil!

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Hornet posted this 5 weeks ago

I was reading Ness's Practical Dope on the .22 and he mentions that H. Guy Loverin said to seat the 225438 to NOT touch the rifling. He recommended 3.0 Grains of Unique for squirrel, etc and said they'd gone as high as 10.5 grains of 2400 (2750 FPS!!). Something to think about.

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RicinYakima posted this 5 weeks ago

I did also. But it was published in 1947, before they made the cases 10% thicker and reduced the case volume. I'm going to start with your loads and work my way up in the Savage 23D. Ken Waters liked 3.3 grains of Unique also with SR primers. 

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