Subsonic 308 w/ SR4759

[kombayotch]

Ok, before people start coming out of the woodwork saying: "Trailboss, Trailboss, Trailboss..."; I've been around the block with fast burning pistol powders in subs (including Trailboss). What I have found is that in a longer barrel (over 20" typically for a 308 vs. under 16.25 for a Whisper), you need some form of lubrication in order to get consistency. Without it, the first round takes a big dump (CBS or letting the barrel cool). SDs can get horribly bad depending on how long the barrel sits between shots. I get good groups if I disregard the CBS and shoot the group quickly right after. But, I don't consider that to be reliable consistency. It seems to be common:

http://www.ebr-inc.net/articles_subsonics-do-not-like-long-barrels.html

I don't believe the lack of consistency has anything to do with case capacity. Case capacity only limits powder choice due to SEE. The fact that lube of some form (oil, wax, moly, hBN) will make the load consistent, logically says that case capacity is not the issue. What that says is that the fast burning pistol powder is only pushing the bullet for a short length of the barrel and then all that the bullet is seeing is friction. The friction can vary a lot as the bore expands thermally and/or becomes fouled. Lube is reducing that friction and making it less of a factor.

I think the solution to better consistency with subsonics in standard length 308 barrels is the use of a slower burning powder that will continue to push the bullet for a longer length of the barrel. This should, in theory give better consistency. The downside is that powder charges will be larger and a larger volume of gas will be produced, which may make the load slightly louder than one using a fast pistol powder.

When browsing the IMR website, one of the slower pistol powders caught my eye.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"><span style="font-weight: bold">SR 4659</span>
This bulky powder really shines as a reduced load propellant for rifle cartridges. Its large grain size gives good loading density for reduced loads, enhancing velocity uniformity.</div></div>
They have reduced load data for 300 Savage:
180gr. SP 2.600" COAL 22.5gr. 1910fps. 45,500 CUP

They only list Trailboss for reduced loads also, not for subsonics. But we know that it works.

I also found this in our Reloading Depot:
308 Loads
10" Shillen 1/8 --pistol
240 SMK
15.7 IMR SR 4759
Win cases and WLRM primers
1" group at 100
1060 fps
very consistent, not temp or position sensitive


Accurate Arms XMR 5744 looks like it could also work.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"><span style="font-weight: bold">A-5744</span>
An extremely fast burning, double-base, extruded powder. This unique powder can be used in a wide range of rifle calibers and magnum handguns. It is characterized by excellent ignition and consistency over a very wide performance range. Superior ignition characteristics make 5744 an excellent choice for reduced loads in many rifle calibers and in large capacity black powder cartridges such as the 45-70 through 45-120 and 50-90 through 50-120.</div></div>
They list data for a lead bullets in 308 Win:
160 LYM RNGC 19.5gr. 1650fps.
200 LYM RNGC 18.0gr. 1550fps.

Thought is that one of these may be the ticket for 220 RN in a 1-10" barrel.

Has anyone tried either of these powders for subsonics in 308?

 

[Queequeg]

Re: Subsonic 308 w/ SR4759 or AA5744?

Dr. K,

Another great post. I have two daughters who might just take a little more of a shine to the .308, .270 and .30-06 if the recoil was eased into a little.

I have been sitting on a pound of SR 4759 for about 5 years. I've never gotten around to using it though I was considering it in the .45 Colt since the burn rate is so close to H-110, W296, as well as H and IMR 4227. These latter powders are great +P powders for modern revolvers and lever guns so chambered and I thought it might follow that this powder might be well suited for it as well. As I found no reliable data for this choice, I have not loaded the .45 Colt with it, though I think it's larger mass would optimize the large case capacity.

Additionally, there was a recent handloader column by Dave Scovill where he flat out stated he would never make any recommendations for the use of SR4759 because of the possibility of confusion with SR4756, which he also abstains from discussing. There have apparently been many surprising results attending to said confusion...

Anyway, as always, I look forward to your efforts.

 

[coldboremiracle]

Re: Subsonic 308 w/ SR4759 or AA5744?

Great information, and thinking, Iam very interested in the results of your testing. I shoot 220 RN out of a 24 inch 10 twist barrel, I tried TB but the case filled up before I got to my desired 1050, so I tried some clays, 10.5 gr and it works great, but it tends to be a little sensitive. So I understand your search for the better powder, and I hope one of these works out.

 

[kombayotch]

Re: Subsonic 308 w/ SR4759 or AA5744?

I picked up a pound of SR4759. I chose it over A5744 to begin with because it was cheaper locally and because A5744 is double base, whereas SR4759 is single based. Which should make SR4759 more temperature stable. Its a pretty interesting powder; basically the extruded tubular version of Trailboss. Looks like an RL-17 kernel with a hole through it. It works nicely in the Chargemaster.

12 gr. fills up a 308 case about 1/3 of the length. 15 gr. is at nearly half. I'm thinking this is the range I need to be in for the 220 RN or a 190 SMK.

Confusion isn't really a good reason not to try it since I will probably never have SR4756 laying around and when I go to buy the powder, there is quite a difference visually between SR4759's brown label and the bright lime green one on SR4756. Gotta love that color coding...

 

[kombayotch]

Re: Subsonic 308 w/ SR4759 or AA5744?

Some density numbers for various powders:

Trailboss: 0.209 cc/gr.
N32C: 0.154 cc/gr. (Lapua SS powder? bulkier than N320 and has less energy so you should need more)
Red Dot: 0.141 cc/gr.
Solo 1250: 0.126 cc/gr. (AA has loads for .223 subsonic, quite slow burning)
N320: 0.118 cc/gr.
SR4759: 0.099 cc/gr.
Titegroup: 0.0848
A5744: 0.070 cc/gr.

Some companies give Bulk Density in grams/liter (lower = bulkier), some give Volumetric Material Density in cubic centimeters/grain (higher = bulkier). Not just different units, but inverted. There are other combinations of g, gr, cc and l, but those two are the most common I have come across.

1 liter = 1000 cc
1 gram = 15.4324 grains
cc/gr. = 1/((g/l) * 0.0154)

Here is Lee's chart for most powders: http://www.leeprecision.com/cgi-data/instruct/VMD%27S.pdf
Numbers are a bit different than above (different sources above).

 

[seafire]

Re: Subsonic 308 w/ SR4759 or AA5744?

I use SR 4759 for a lot of my loads...

always consistent and accurate...

5744 has too big of a bang each time you pull the trigger..

 

[kombayotch]

Re: Subsonic 308 w/ SR4759 or AA5744?

Are these loads subsonic? Got any recipes to share?

 

[cinosbus]

Re: Subsonic 308 w/ SR4759 or AA5744?

It should work. XMR-5744 is used in the Savage smokeless capable muzzle loaders. You should also be able to find some loads for SR4759 for reduced .30-06 loads that will get you in the ball park - that's what it was designed for. Try Speer manuals.

 

[bowslngr]

Re: Subsonic 308 w/ SR4759 or AA5744?

I tried SR 4759 for a reduced load in 308 (not sub-sonic, more like 1700-1800 fps) a while ago and gave up on it due to wildly eratic velocities. Maybe it will prove to be more consistent in lower charges/velocities.

 

[kombayotch]

Re: Subsonic 308 w/ SR4759 or AA5744?

Got out today and results look very promising. Started by running a few tests with my subsonic Titegroup load (works better than Trailboss). Confrimed once again that if I leave the barrel sit for a few minutes before shooting, the first round hits several inches below when no lube is used. Tried it in both my 26" Bartlein 1-11.25" and 22" Broughton 1-10".

This didn't happen with SR4759. I fired a few rounds to find the right velocity. Then I let the rifle sit while I made up the next test set or fired a few groups with the .22LR. Drilling the primer hole helped with the WLR primers, but wasn't necessary with 215M. SR 4759 seems to eliminate the first round drop in the longer barrels.

The only problem is that the bullets were key-holing.

I will have to try it with some lighter bullets.

 

[kombayotch]

Re: Subsonic 308 w/ SR4759 or AA5744?

Did some testing with lighter bullets today. Results were the same as with Titegroup and Trailboss. I believe the pressure is just too low to get a consistent burn. Tried a 170 FP, 180 PSP and 190 SMK (forward and backwards).

The 190 SMK bullets loaded backwards were hitting the paper sideways at 100 yards. You could actually see them tumbling through the air through the scope. Loaded normally, they were showing a bit of key-holing.

A friend arrived with some 208 AMAX bullets, so I gave those a shot. Like the 220 RN, velocities were extremely stable (no first round drop) and groups were nice and small. However, they were also key-holing. This powder seems to work extremely well with the heavy bullets for subsonics. A 1-9" or 1-8" barrel should fix the key-holing.

 

[cinosbus]

Re: Subsonic 308 w/ SR4759 or AA5744?

Anybody tried the Lapua subsonic 200gr bullet in a 1:11 or 1:12 twist?

http://www.grafs.com/retail/catalog/product/productId/9566

 

[kombayotch]

Re: Subsonic 308 w/ SR4759 or AA5744?

Oh yeah! Damn! Forgot about that one... Never tried it with fast pistol powder though either. So, I don't know if you get the first round drop with that one. I might be heavy enough for the SR4759.

 

[cinosbus]

Re: Subsonic 308 w/ SR4759 or AA5744?

Reviews are mixed on that one with anything slower than a 1:10 twist. I will probably try some someday.

 

[cinosbus]

Re: Subsonic 308 w/ SR4759 or AA5744?

You might try crimping with a LEE factory crimp die with the slower powders, but some people warn against crimping with reduced loads.

 

[former naval person]

Re: Subsonic 308 w/ SR4759 or AA5744?

Since the "subsonic" bullets are going to be "subsonic" and lead bullets work well at those speeds...and they are lubed anyway, why not just use a hard cast lead bullet tailored to your barrel and twist? Do you need an expensive jacketed bullet for purpose? Educate me. Thanks, FNP

 

[RTH1800]

Re: Subsonic 308 w/ SR4759 or AA5744?

I use IMR 4227 and IMR 4759 with SS loads. I do modify the primer pocket for consistant ignition. Lapua SS 200 grain bullets. I can duplicate the Lapua factory SS load with a bit more uniform velocity.
I would not reccoment shooting cast bullets through a suppressor. I ruined one and have heard that this is common. If the bullet "strips" in the fast twist lands you are done. Fed 215 Match primer. Shoots accurate to 200 yards. Kills well. I did have trouble with the 220 Spear killing well. NOt sure why. The Lapua bullet is effective. 1/10 twist.

 

[former naval person]

Re: Subsonic 308 w/ SR4759 or AA5744?

He had mentioned a cast bullet load which is why I asked. I agree about the can. I had a .454 Casull once which was Magnaported. Shot beautifully with jacketed, but with heavy cast loads, the ports blew all the lube off and after 12 rounds the last inch of the barrel was lead plated. If he isn't using a can, he can really get down low on speed. If you go too low with a jacketed bullet they stick in the barrel and are hell to get out without ruining the barrel. Lead bullets, on the other hand, will stick at a too low pressure load, but are relatively easy to push out. JMHO

 

[cinosbus]

Re: Subsonic 308 w/ SR4759 or AA5744?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: rth1800</div><div class="ubbcode-body">I use IMR 4227 and IMR 4759 with SS loads. I do modify the primer pocket for consistant ignition. Lapua SS 200 grain bullets. I can duplicate the Lapua factory SS load with a bit more uniform velocity.
I would not reccoment shooting cast bullets through a suppressor. I ruined one and have heard that this is common. If the bullet "strips" in the fast twist lands you are done. Fed 215 Match primer. Shoots accurate to 200 yards. Kills well. I did have trouble with the 220 Spear killing well. NOt sure why. The Lapua bullet is effective. 1/10 twist. </div></div>

Care to get us in the ballpark with your charge weights?

How much do you drill the primer?

 

[RTH1800]

Re: Subsonic 308 w/ SR4759 or AA5744?

I used 13 grains with the 4227, which I liked best. Start low, around 11 grains and work up on a chronograph. Flash holes were bored to just leave a rim large enough to hold the primer. I would guess about .125" and deburr. F 215 primer. The mag primer is one of the keys to consistant velocity. Lapua does not modify SS cases. They do color the bases blue, which is a very good Idea, that I have used. They even show up at night, compared to non colored ones.