Magnum LR Primers on standard ammo.

[Jorlcrin]

I remember a while back; someone talking about using magnum primers in Large Rifle ammo.

I just found I have about 700 CCI LR Magnum primers (CCI No:-250), and was thinking about using them on my .308 loads.
Given availability of things like primers is a bit Hit & Miss, I thought these could be useful, if they can be used safely.

I thought I read that I need to dial the powder charge back a little?
Is that correct?
If so, by how much?

[Larry]

You can do it but it may have unintended outcomes. Like less accuracy. The 308 is a good example. Target shooters to improve accuracy have found that using small rifle primers and a smaller flash hole give better results. while still maintaining full powder burn and velocity. In fact it is the velocity that is much more consistent.

[Jorlcrin]

Accuracy wont be super-critical for these loads; all of these shots are going to be in the 50-250 metres range while hunting ferals.

It's more about whether I can use them up; shame to waste them, and I dont have anything that runs magnum LR primers.

[bladeracer]

I remember a while back; someone talking about using magnum primers in Large Rifle ammo.

I just found I have about 700 CCI LR Magnum primers (CCI No:-250), and was thinking about using them on my .308 loads.
Given availability of things like primers is a bit Hit & Miss, I thought these could be useful, if they can be used safely.

I thought I read that I need to dial the powder charge back a little?
Is that correct?
If so, by how much?

I loaded a batch of 8x57mm with LR, LRM and some old Federal LR I bought in 1983, all with the same load and I saw no difference between them on paper.
It's _possible_ that if you're using the lightest available LR primer and you swap to the hottest possible LRM primer that you might see a measurable difference on a chronograph, but I don't believe you're going to do any damage unless you're already running the ragged edge of safety. Likewise, there's also a possibility that it might be enough of a difference to pop you out of your accuracy node, but unlikely I think. Only way you'll know for sure is to load a few and shoot them for a group over the chronograph.

It's also possible that there might be people desperately wanting LRM's that might swap you for LR, perhaps even a favourable swap for you, which might be a consideration.

[Jorlcrin]

I did consider that, but I'm living in the middle of nowhere, and not likely going to be anywhere to swap primers with anyone in the near future.

I think I'll do as you suggest, and see if the LabRadar is still alive enough to tell me what I want to know..
Failing that, I think I'll just fire them off and persecute some ferals...

Thanks for the info.

[Cooper]

I remember a while back; someone talking about using magnum primers in Large Rifle ammo.

I just found I have about 700 CCI LR Magnum primers (CCI No:-250), and was thinking about using them on my .308 loads.
Given availability of things like primers is a bit Hit & Miss, I thought these could be useful, if they can be used safely.

I thought I read that I need to dial the powder charge back a little?
Is that correct?
If so, by how much?

If I was doing it and I was near to max load I’d just drop the load by 1gr and check. I found that switching to magnum primer with a slow burning powder the velocity actually reduced when checking velocity with chronograph. If you have a chronograph definitely pretty easy to see what’s going on by checking velocity.

[rc42]

Despite the common anecdotes and reports from very poor test setups, when measured scientifically different primers have been repeatedly shown to make NO measurable difference to muzzle velocity, if there is a small difference it's well within the normal round to round variation even with the most carefully measured powder and seating.

Magnum primers have thicker cup material so that they can withstand higher pressures but also need to be struck harder by the firing pin. Sometimes they have a little more primer material which burns slightly longer or hotter to help ignite slow powder but this has negligible effect on the pressure curve or projectile velocity at the muzzle.

[deye243]

Cci 200 and 250 primers have a primer cup that is 0.027"

Screenshot_20240821_233235_Gallery.jpg (181.38 KiB) Viewed 2615 times

[SCJ429]

I have used Magnum primers in a 243 shooting heavy VLD projectiles. They gave me a better ES than BR2 primers.
The 243 uses the same case design as your 308.

[Faedy]

I use them in both my .308's regularly with no issues

[Wapiti]

You can do it but it may have unintended outcomes. Like less accuracy. The 308 is a good example. Target shooters to improve accuracy have found that using small rifle primers and a smaller flash hole give better results. while still maintaining full powder burn and velocity. In fact it is the velocity that is much more consistent.

I asked at my local gunshop about this, and the guy three is a known long-range big-bore shooter.
He reckons that with the 308 and the small rifle primer cases, that you must use "small rifle magnum" primers. He said people have gotten into dramas on the range using normal small-rifle, having partial detonations and wildly varying velocities in load testing. This was because, he said, the standard small-rifle were not consistently detonating charges over 40 grains or powder in a consistent pressure curve/burn and this was due to them not being designed for this amount of stick powder... and that small rifle Magnum was.
And that the magnum primers did indeed solve this because they had a hotter/longer flame time.
He reckoned the thicker/higher tensile cup story is not true, and gave the example of the tiny surface area the pressure is trying to act upon in the rifle cases.

Now, which of all the stories out there are made up? Who do you believe?
I've seen super fast video online between different primers showing obviously larger flashes from the magnum primers within the same brands.

I asked this because there is a brand of US-made premium 308 cases that take small rifle primers, designed by the maker to only use CCI small rifle magnum primers, that people have been loading at up to 300WM velocities, because of their innovative brass strength and the tiny primer making the case head much stronger. That is a fact, so who/which of all this info is untrue, just being repeated to confuse everyone?

[Larry]

Nope all the guys in the clubs and the shooting lines I have been on which is quite a few shooting F Class have all used Lapua Small Flash hole brass and either CCi BR4 primers or Fedral Gold Match. I have always used BR4. Sorry but your man either surveyed the wrong group of people of has his wires crossed.

[Wyliecoyote]

I have done the small versus the large rifle primer test in 308. To get the same speed you need more powder about a half to one grain, when using SRPs and that goes with magnum SRPs as well. Accuracy i couldn't split with either where this test was done in a rail gun to remove human error. What was interesting was the velocity. With LRPs the ES was around 20 fps using the 175 grain MatchKing. With the SRPs, the ES was in the low teens or better but the groups opened up. This phenomena is usual as bullet exit time is more important where bullets exiting at precisely the same barrel time group better even though they vary slightly in speed. Then bullets at the same speed but leaving the barrel at different intervals group poorly. Hence the common question of "why is my rifle grouping so poorly but the ES and SDs are in single digits?"
There is a point where brass will yield. That point is irrespective of primer pocket size. But SRP pockets do last longer in 308 brass when you keep to safe pressure levels. You can lose any piece of brass if over pressurised.

[Wapiti]

Appreciate the comments on my post, I had this brainstorm a few months ago and as I didn't know anything about SRP's in a 308, I asked where I could.
You can only ask if you don't know, instead of weecking something or wasting time.
Where we are, the nearest gunshop is a 3hr round trip (yeah, there's phones now) and it's not like there's too many people with the time or interest to do that stuff out here. It was actually a silly idea anyway for me and wasn't going to advantage me in any way anyhow.