6.5 SAUM, AKA Gap 4S In Long Action

[carlsbad]

I just built one and am surprised I can't find loads for a long freebore. Everything I see on several forums is designed for the Short Action magazine-limited freebore of about .081" which gives you a COAL around 2.910. I cut my freebore to .185 for 140 hybrids and expect my coal to be around 3.015. Dummy rounds feed well from 338 LM magazine but I'm getting a couple of 300 WM magazines that should be more reliable.

Anybody else doing this? If so, would you share your loads?

thanks,
Jerry

 

[Kurz]

Doing a little math, your cartridge OAL is only about 0.105" longer than the standard cartridge OAL. This should allow you to start with some of the better medium loads for the standard cartridge length and work up your ladder or OCW from there. The difference you'll find is not that significant.

Enjoy the process!

 

[carlsbad]

by medium you mean 60-61 gn of H1000?

 

[Kurz]

In order to preserve some safety factor, yes, 59 - 60 grains of H-1000 should be a good start. As I stated above, there isn't that much of a difference between the two capacities. You may notice a slight increase in velocity but it shouldn't be significant. You can boost the velocity by using a double base powder instead but the barrel savers will howl about burning out the barrel.

Enjoy!

 

[Danny1788]

jerry how long is your barrel? more specs and picture of your new build??

 

[carlsbad]

I'll get a photo later tonight or this weekend. 30" barrel. thanks for your help. Jerry

 

[NickB1075]

Very nice looking rifle!! What stock is That?

Thanks
Nick

 

[carlsbad]

Mcmillan "prone" with adjustable buttstock.

Link

 

[fredo]

A driving point behind GAP developing and designing their "4s" 6.5 SAUM variant was to maximize performance from a magazine fed short action.

The original "4s" reamer started with .104FB, IIRC, and was shortened to .081FB for better use with hybrids and JLKs. Now,with the new ELD line of bullets from Hornady, they're back to recommending the longer FB to suit them...

In case you didn't know, Hornady makes "6.5GAP 4s" brass, therefore not a surprise they'd want those ELD bullets to get the freebore they like best.

I guess you might eeek out some extra useable capacity from a longer throated LA and 140gr+ bullets?

For comparison, I'm running a (moly)140JLK @3070 from a 24" barrel with 62gr H1000. If that were a 30" barrel, bet it'd be dang close to 3200...

Beautiful rifle!

 

[carlsbad]

Fredo,
Thanks. Yes, I knew that was the driving force behind development of the 4S but since it has been so successful, I'm building it for use where I have no need for restriction to short action. In fact, probably a lot of us have an unused long action receiver sitting around with the correct bolt face making it an easy build. this one is built on a beautiful old Remington action with scrollwork that I picked up cheap because it had been chambered in 7mm Remington Ultra magnum with a sporter barrel and was breaking too many collarbones. I trued it up and expect good performance.

So I thought I wouldn't be the first to do this, and I still suspect others are doing it. But I haven't found them. My thoughts are that the extra case capacity and ability to seat the bullet farther forward, away from the shoulder should be a positive. The guys shooting 140s with the .081 freebore are jamming them in there pretty far. I have a box of 147 ELDs on the way for testing.

I picked up some Hornady 4S brass when it came back in stock. I had bought a large lot of 7 SAUM brass on Gunbroker but only received half of it and after a big mess of arguing I finally got my money back.

My one concern was feeding but my dummy round seems to feed fine from a 338LM magazine. I'm going to get a 300 WM magazine and it should feed even better with longer feed lips. SS feeds fine sitting on top of the magazine. I'm using Accurate Mag magazines and the depression in the middle of the polymer follower provides a nice seat for the round to be picked up.

Next time I go to the range is June 3 so I'll have some test results then.

--Jerry

 

[ncboiler]

RL 26 should be good in the SAUM as well. I have a pound that I was using for my 6 Comp Match but I want to load up some SAUM ammo with it as well. It could show some pretty impressive speed.

 

[germanlongbow]

I've had better luck with Retumbo than H1000 in my saum. I started with 0.081 freebore with original reamer and barrel. Bought a new barrel (30 in) and throated the standard 0.081 to 0.120. I gave up on H1000 after 400 rounds of load testing. Nothing consistent in grouping. Retumbo has worked well with Sd in 6-11 fps range. Shoots great out to 860 yards. Plan on pushing furher when time permits.