6mm Magnum vs 6 CM +P

[B_Reynolds_AK]

Primer pockets generally hold up a bit better in srp when loading warm. I've had a few hang fires in sub zero temps with lapua srp brass with slow powders like rl26 in my 22cm. Lapua uses small flash hole, Alpha uses large flash hole, haven't had the same issue with alpha brass. Moving to a faster burning powder in the lapua brass remedied the issue but did lose some velocity.

Copy that. Thank you.

 

[z987k]

The 6 UM and 6 PRC are the top tier 6mm cartridges at the moment. The external ballistics are great and those building them
are accepting of the sub 1,000 rd barrel life.

Defensive Edge +P seems to get mixed reviews. You gain up to 120 fps at the expense of less barrel life and throat erosion, which seems to be the main argument that people make against it.

I really like my 6 CM, with its AnTi X short action, standard bolt face, easy reloading and factory ammunition. As well as being able to spin on other .308 based cartridges such as 338 Fed.

If I was accepting of a hunting barrel with a shorter barrel life, why should I not just have a light contour 18" or 20" barrel spun up in 6 CM +P to be able to shoot 108-115g projectiles at around 3,000 fps, rather than go with a 6 Magnum? My heavier, standard 6 CM, barrel would be for training.

What bullets are you using in your 338F? It seems like most of the lighter 338s have left the market.

 

[Houseminer]

I would go 6.5. This is coming from a 6mm shooter. Negligible recoil either way. 6.5 gets you better barrel life and better splash on misses. Just shot out to a mile with both calibers this week and was very surprised that they both laid hits on a 1.5 moa Target but also how much more dirt the 142gr bullet kicked up compared to my 115gr.

 

[B_Reynolds_AK]

What bullets are you using in your 338F? It seems like most of the lighter 338s have left the market.

Used Federal Trophy Copper 200 and Federal Fusion 200 in the past.
Now that I’m reloading, I’ve loaded up ammo with Hammer Bullets 186 Shock Hammers.
Big ol’ hollow point on the front of that thing and no B.C. Haha.

 

[B_Reynolds_AK]

I would go 6.5. This is coming from a 6mm shooter. Negligible recoil either way. 6.5 gets you better barrel life and better splash on misses. Just shot out to a mile with both calibers this week and was very surprised that they both laid hits on a 1.5 moa Target but also how much more dirt the 142gr bullet kicked up compared to my 115gr.

I’ve used a 6.5 CM for a decade now as well. The benefits that you are describing are not what I’m looking for though. Recoil is noticeable between the two and splashes at 1200 yards are just fine with the 6mm for me.

 

[khuber84]

I would go 6.5. This is coming from a 6mm shooter. Negligible recoil either way. 6.5 gets you better barrel life and better splash on misses. Just shot out to a mile with both calibers this week and was very surprised that they both laid hits on a 1.5 moa Target but also how much more dirt the 142gr bullet kicked up compared to my 115gr.

Op is talking 18-20" barrels. 6.5cm velocity in that short a barrel is 2650-2700 on the top side. 6mm at that length is still 2900-3000. I have equal weight 6cm and 65cm, shooting the heaviest for class bullets in upper velocity nodes, say a 115dtac VS a 153 Berger, the 65 def has more noticeable recoil. Splash at a mile makes no difference in a hunting rifle. 99% of hunters have no business shooting game past 500y. 99.9% past 1000y.

 

[Itsalongshot]

I’ve been considering a 6creed +p or 6 PRC. This thread has helped steer me to 6prc or just a plan 6 creed.

 

[B_Reynolds_AK]

I’ve been considering a 6creed +p or 6 PRC. This thread has helped steer me to 6prc or just a plan 6 creed.

Same. Had another barrel spun up in a 18” 6 CM. Plenty of velocity to expand at 800+ yards.

 

[Sadler]

FWIW I had the same idea last year and called unknown and talked to Blaine. He recommended against it. So I’m sticking to my 16” 6 creed and will be loading up some 109s this weekend.

 

[B_Reynolds_AK]

FWIW I had the same idea last year and called unknown and talked to Blaine. He recommended against it. So I’m sticking to my 16” 6 creed and will be loading up some 109s this weekend.

Crazy how far even a 16” 6CM is effective to. Such an effective cartridge with high BC bullets.

 

[Sadler]

Crazy how far even a 16” 6CM is effective to. Such an effective cartridge with high BC bullets.

I know. Just shooting factory 108 eldms I’m approaching 2700fps. That’s plenty for how far I’m capable but I can’t help myself. I want to see what these 109s can do

 

[wind gypsy]

I’m not sure that’s accurate is it? From the research I did it seems most report 2900 is about the max to expect with a 20” barrel without going over pressure. This thread has some good real world input from folks running 6 creed with short barrels. That was what steered me towards a 6 PRC build with a shorter barrel as I wanted to be closer to 3100 fps with the 108’s and over 3000 with 115’s.

I think with N555 or RL26 with Hornady, Lapua, or Alpha brass, 2900 COULD be a reasonable load but maybe a bad idea to go into a new barrel expecting that? My current 18" kampfeld chambered benchmark would run there pretty happily until it's approaching 100 rounds after a cleaning and then it starts getting sticky bolt lift with even 100 FPS lower so I don't know what the deal is with that. 43.0 gr N555 gets me 2850ish FPS in alpha or lapua brass with the 106 TAP, 108 EH, 109 ELD class bullets. VV book max behind a 108EH is 43.7 i believe. Have another 18" prefit on order from PVA so we'll see if this fouling sensitivity is a one off.

 

[VirginiaBeach]

Ben,

I shoot exclusively SRP in all of my Creedmoor and Dasher rounds and have never had any ignition issues down to some extremely low temps in Montana over thousands of rounds. I’m not sure how real the “LRP is more reliable for ignition” argument is. The first time I remember hearing it was speculation that it could be an issue and it was in reference to David Tubb developing the 6xc.

The idea of “loading down” some magnum rounds is thrown around quite a bit to reduce recoil for practice but in my opinion, is not a real feasible option because:
1. In my experience, overbore magnums aren’t the most forgiving thing to reload for so you may not be dealing with something where you can easily swap to a bulkier powder that still shoots accurately in your rifle but with less powder and still adequate case fill.

2. It’s twice as much work to develop two different loads so most people don’t do it

3. If you want a reduced recoil trainer get a .223 barrel and bolt(which you probably already have) you’re going to want one anyway

I haven’t run the numbers yet, but I’m betting a 6 cm going 3000 fps at your DA with a 109 eldm will maintain 1800 fps out to as far as you want to shoot game. Will an 18” barrel get you there? Maybe not but probably 20-21” of barrel.

 

[khuber84]

I love short barrels, but I don't like sacrificing speed. My new ones a 22" 6cm. Also have a 24" 6 Saum. If sierra would ever make a run of 95gr tmk again, I'd ponder an 18-20" 6br or 6gt. My shortest rifles an 18" 22cm that has no problems running 80s at 3250-3300

 

[Lawnboi]

For a hunting rifle get LRP creedmoor brass.

I have experienced hang fires with h4350 in the creedmoor cases mostly with srp alpha.

 

[Lawnboi]

I think with N555 or RL26 with Hornady, Lapua, or Alpha brass, 2900 COULD be a reasonable load but maybe a bad idea to go into a new barrel expecting that? My current 18" kampfeld chambered benchmark would run there pretty happily until it's approaching 100 rounds after a cleaning and then it starts getting sticky bolt lift with even 100 FPS lower so I don't know what the deal is with that. 43.0 gr N555 gets me 2850ish FPS in alpha or lapua brass with the 106 TAP, 108 EH, 109 ELD class bullets. VV book max behind a 108EH is 43.7 i believe. Have another 18" prefit on order from PVA so we'll see if this fouling sensitivity is a one off.

His standard 6 creed freebore is long! To the point I could make 105 hybrids going 2900 to low in pressure to seal the chamber. That might help

 

[wind gypsy]

His standard 6 creed freebore is long! To the point I could make 105 hybrids going 2900 to low in pressure to seal the chamber.

Good!

 

[Flyjunky]

For a hunting rifle get LRP creedmoor brass.

I have experienced hang fires with h4350 in the creedmoor cases mostly with srp alpha.

Would going to cci450, srp magnums, help with that? I’ve read people using those in tough conditions.

 

[Lawnboi]

Would going to cci450, srp magnums, help with that? I’ve read people using those in tough conditions.

That’s what I used when I had hang fires.

I didn’t believe it either until it happened.

 

[Flyjunky]

That’s what I used when I had hang fires.

I didn’t believe it either until it happened.

Good info, thanks