4759 in the 7TC/U

[jhalcott]

I tried 5 rounds each of 15.5,17.5 and 19.5 grains of sr4759 with the 287405 and 135 grain "soup can" 135 grain bullet today. The 21" TC carbine with 2x7 burris scope was the gun. Off sand bags, front and rear, the best 50 yard "groups" were about 4 inches with a flyer or 2 to make them 6" patterns. One of the 150 grain 287405's went thru the paper side ways. I do NOT believe the bullets are the problem as I have used them in other 7mm barrels with MUCH better results.This IS my FIRST time with this powder though! This barrel likes the J-word slugs in the 120 to 139 grain range. The bore seems to be quite dirty from this 4759,I ran a patch thru it between loads. They came out nasty!

[44man]

I wonder if it is boolit match to the barrel??? :confused: I use 18.4 gr's in the 7-R which is a 30-30 case necked down. I use 18 in the 7BR. Both with the Hornady 154 gr bullets. Accuracy is extreme with many 200 meter groups under 1".
That is one powder I would NOT be without but I don't know the case size limit for it to work. It is bulky for reduced rifle loads. You might not be getting it up to pressure. That little .223 case might just be too small.
It is the ONLY powder that works in my 45-70 BFR revolver too.

[Shuz]

Have you tried H-322 in the 7mmTCU?

[jhalcott]

Yes Shuz, BUT I have a new 5 pound can of 4759!
44, I seemed to be getting PLENTY of pressure . Judging from tight extraction and primer appearance, the upper loads were quite PEPPY! The gas checks were seated into the case more than I like, but I had to do this for closing the action.

[fourarmed]

If you are getting keyholing, it is very unlikely that the powder is the problem. A bullet/barrel problem would be my bet. In my experience, 4759 works very well in most of the silhouette cartridges with cast bullets.

[Junior1942]

I bet fast twist and high velocity is your problem.

[44man]

Yes Shuz, BUT I have a new 5 pound can of 4759!
44, I seemed to be getting PLENTY of pressure . Judging from tight extraction and primer appearance, the upper loads were quite PEPPY! The gas checks were seated into the case more than I like, but I had to do this for closing the action.
OK, that means it is boolit, velocity and twist issues. Try reducing the loads.
Sorry that I don't have the caliber so I can be of more help.
The powder itself rarely causes the problems you are having unless it changes velocity too much.

[jhalcott]

15.5 grains is the starting load for this in MY books with these bullets. BOTH bullets gave large irregular groups with 4759 and have shot them better with other powders. Even 4198 and 748 worked better! The only other thing might be a change from cci to rem bench rest primers. I'm going to try 4759 in another case, the book shows 16 to 20 grains with a 135 cast(gc) in the 7-30 Waters. If the case is size the problem, maybe it will work in there.!(?)

[TCLouis]

18.0 SR4759 is the max listed for a 150 grain (311440) boolit in the 30-30 according to to the Lyman Cast Manual.

19.5 may just be a "bit" too hot!

[jhalcott]

In the "Contender" book and Lymans 47th edition 19.5 and 20 grains are listed. This leaves a bullet /bore condition as a cause. Since these bullets worked in other loads ,I'm thinking MAYBE a coating of LLA over the present lube (NRA50/50) could work!(?) Reviewing my notes, I used LLA with the other powders. I was out of FWFL at that time.
19.5 DOES seem to be at the top of the charge level. The primers were all flattened and the cases came out reluctantly after firing. There was a noticeable resistance when opening the contender action that wasn't there with the lower charges. Accuracy at all levels with both bullets was 4"+ grroups (5 shots)!

[BABore]

Check your throat length in that T/C. They are notorious for looooooong throats. My buddy's 357 Herrett wouldn't should cast worth a hoot, but is a tack driver with jacketed. A chamber cast showed a 0.400" long throat. Also shoot a couple boolits into something soft so you can recover them. Look at the width of the riling marks near the nose. Should be a dead give-away if she's skidding after a long jump.

[jhalcott]

BA, you seem to have hit it! After lubing with NRA 50/50 and LLA, I loaded 10 rounds each with the same 18.5 grain charge of 4759. I seated the 287405's To seat against the rifling. The "soup can's" are a bit shorter but seated with about a caliber into the neck. The 2nd shot was a flier, the bags slipped as I pulled the trigger. The other 4 grouped well under an inch. the flier was 1 1/4" high right. The entire group was still at 2". The 287405 went into a wide 4"x 2" high group. The cases started to become hard to chamber??. I fired 7 of these and s6topped as pressure was becoming evident. I did NOT clean between groups . The next 5 "soup cans" went into a group similar to the 287405's. Smaller but similar! None keyholed.