Use of magnum primers

[robertWperret]

I noticed that there are quite a few reloaders posting that they are using magnum primers in their 6.5 grendel loads. In my new Odin works upper I notice I get groups that seem like the groups spread horizontally when using IMR 8208 xbr powder. I am currently using WW small rifle primers and new Starline brass. Would the use of mag primers tighten up my groups?

[204 AR]

Primers could make a difference, sometimes horizontal is seating depth.

[grayfox]

When I see horizontal I think it's usually shooter or something weaving the barrel horizontally, trigger pull, palm push, etc. Vertical usually means MV changes.
That said cci450's could help you out, but as it's a different/hotter primer you may need to work back up to your loads.

[VASCAR2]

The reason for the use of magnum primers is the floating firing pin in the AR-15. If you ever extract a live cartridge out of an AR-15 chamber you’ll see a slight primer hit. The magnum primers and many match primers have thicker primer cups which resist slam fires. CCI 450, CCI 41, BR4, Remington Magnum small rifle primers and Federal AR primers have thicker cups.

[StoneHendge]

I was fighting horizontal stringing in the Spring and it was related to not having a consistent and relaxed grip.

[Rcurry2069]

When I see horizontal I think it's usually shooter or something weaving the barrel horizontally, trigger pull, palm push, etc. Vertical usually means MV changes.
That said cci450's could help you out, but as it's a different/hotter primer you may need to work back up to your loads.

Correct answer

[soloelcap]

I switched over to CCI 450 primers from Rem 7 1/2's in both my 6mm AR barreled guns per the recommendation of a couple guys Rich and Greg. My groups at 100 yrd got tighter, mine and my wife's scores at 600 yrds.got better. Same load, case and Oal powders H4895 and XBR.

[Zeus]

....inconsistent cheek-weld and improperly adjust parallax (not focus) can cause problems too.

I can also say that I use CCI magnum primers in all my AR15 loads.....

[Lemonaid]

I was researching why most everyone was using CCI 450's and if it might be detrimental to accuracy. The primers used by the following companies in their posted reloading data:

Sierra - Win WSR
Nosler - Rem 7 1/2
Accurate (Western Powders) Win WSR
Hodgen - Fed 205M
Alexander Arms - CCI 450
Speer - Fed Gm 205 MAR

Looking at the early posts in the reloading section it looks like there wasn't much of a difference in accuracy from different primers, but I would like to try some Fed GM 205 MAR for myself when my local sportsman warehouse gets some in stock.

[Klem]

I was researching why most everyone was using CCI 450's and if it might be detrimental to accuracy. The primers used by the following companies in their posted reloading data:

Sierra - Win WSR
Nosler - Rem 7 1/2
Accurate (Western Powders) Win WSR
Hodgen - Fed 205M
Alexander Arms - CCI 450
Speer - Fed Gm 205 MAR

Looking at the early posts in the reloading section it looks like there wasn't much of a difference in accuracy from different primers, but I would like to try some Fed GM 205 MAR for myself when my local sportsman warehouse gets some in stock.

Lemon,

450's have thick cups which resist the unintentional impact of free-floating firing pins.

By all means try different primers but for years we used 450's almost exclusively in local .223 F-Class competition. Absolutely no question as to their consistency.

[Lemonaid]

Thanks for the info Klem! I am an empirical type of person and if it works, it works!
My thinking was that for the size of the Grendel case, it wouldn't really need the extra energy of a magnum primer, and a standard type primer would give a more gentle bullet start with potential better accuracy.
I'm getting pretty good results with the 450's and have a good supply, so it's nice to know they preform so well in competition.

[grayfox]

yeah +1 on Klem. It's not necessarily that there is more energy (or brisance for primers), but that it is consistent. The little extra oomph probably does help. the Grr cartridge is pretty efficient and short powder column, but like the man said, consistent firing (and safe, thicker cup) --- a guy can live with.

edit to add: the firing of the shot is a pretty violent operation, regardless of the primer used...

[Popeye212]

The two that have performed best for me are Fed GM205M and CCI450 and have had zero issues with primers. That said with Murphy alive and well I have just jinxed and put the voodoo on my next range outing......

[babue]

Bill Alexander specified CCI450 primers from the very beginning. I saw no reason to doubt the designer of the 6.5 Grendel as to the best primer to use.

[Popeye212]

Bill Alexander specified CCI450 primers from the very beginning. I saw no reason to doubt the designer of the 6.5 Grendel as to the best primer to use.

Agreed I prefer the 450's bought another 1000 last week.

[Popeye212]

Bill Alexander specified CCI450 primers from the very beginning. I saw no reason to doubt the designer of the 6.5 Grendel as to the best primer to use.

Agreed I prefer the 450's bought another 1000 last week. So far that's all I have used in the Creedmoor.

[65Whelen]

Bill Alexander specified CCI450 primers from the very beginning. I saw no reason to doubt the designer of the 6.5 Grendel as to the best primer to use.

What he said. It's all I use for the Grendel with no regrets.

[Mesa1978]

Bill Alexander specified CCI450 primers from the very beginning. I saw no reason to doubt the designer of the 6.5 Grendel as to the best primer to use.

Yes, this. Thicker cup and accuracy, no reason to tinker.

[Kswhitetails]

I love 7 1/2s. Just bought a brick from a guy going out of business for 27/K. Feel good about it. I've got to go try some 450s, but I can't complain about anything so far, so I'm gonna be in primers a bit longer.

[Ymountainman]

This is true