SWC velocity ceiling

[Marlin Junky]

I was wondering if there might be a velocity ceiling for shooting SWC's accurately from a rifle. My consistency is severely lacking at 1900 to 2000 fps and I haven't been able to isolate any variables yet (e.g., pressure, diameter, lube or twist) as a cause. I don't really have another boolit that'll work in this rifle (a long throated Whelen) but would like to get hold of a Lyman 358627 mold. The best accuracy so far with my boolit in question (260 grain SWC) has been with 26 grains of surplus 4759 for about 1750 fps. I figured a slower powder should be able to drive this boolit a couple hundred fps faster with decent accuracy but so far it hasn't worked out.

MJ

[Larry Gibson]

Is your SWC a GC design or PB design?

I have a 358627 that I'd trade for another mould, whatcha got?

Larry Gibson

[KYCaster]

MJ: I have a Marlin 336 in 35Rem. that shoots five shot 100yd. groups with a Magma 200SWC w/GC into 3.5in. Looks like it could do better with a little work.(three of those in <.5in.) That's at 2055fps. Alloy is 92-6-2.

It does a little better with the Lee 180-RF GB boolit at 2020....pretty consistant at 2.2 to 2.5. Both of these loads use WC846 which doesn't do quite as well as 3031 with most boolits in this gun...I just haven't yet tried these with 3031.

My hunting load is the RCBS 35-200-FP cast of ACWW over 34.5gr. 3031. That gives me 2086fps. and 2.5 to 2.75 groups.

With a little more work I think I can get the SWC to do OK at ~2100 or so.

Jerry

[Marlin Junky]

Is your SWC a GC design or PB design?

I have a 358627 that I'd trade for another mould, whatcha got?

Larry Gibson

It's a very nice 260+ grain SK from Mountain Molds but I don't want to part with it. I'm going to acquire a 14" twist Encore to test the design because I have a feeling the 16" twist I'm currently working with isn't fast enough to stabilize it. I'd be willing to send you some of my SK boolits in exchange for some of your 358627's though.

MJ

[Larry Gibson]

I've not used the 358627 so I don't have any bullets. My Mag 20 went TU the other night and is in the mail back to Lyman so I'm not casting for a few weeks , major sad face :-( .....any other moulds for trade? The mould is in very, very good condition. It's been hardly used if at all. Photo attached, the reddish tint is from the flash I guess, it's not rust..

Larry Gibson

[Marlin Junky]

Larry,

What calibers are you looking for? I just got started with the .35's and I really don't have that many to spare. I may have a couple barely used SAECO .35's (#354 & #399) I might let go but that 358627 needs to be a real cherry if I swap a SAECO mold for it. Can you show me a close-up top view of the blocks and under the sprue plate? I've got a long PB .30 and a 310 grain PB .44. The .30 is an aluminum MM and the .44 is a brass MM.

MJ

[Larry Gibson]

I'm not really looking for another .35 as my one .35 rifle (a M91 Argie rebarreled to .35 Remington) likes the RCBS 200 gr bullet. I've plenty of other SWCs for my .38/357s. Any .41s, .30s, .22s, .32s?

Larry Gibson

[Marlin Junky]

I've got a few .30's. Plain base or gas check? Actually, I think I have a double cavity 311644 that's one of each (one cavity has been PB'd). Let me know so I can take some pictures for you tonight. I'm leaving Sunday morning for a road trip that'll take me away from my shooting equipment for the entire month of November but I'll have my laptop with me the whole time. Feel free to PM me.

MJ

[Marlin Junky]

Larry,

Here's a pic of the 311644 with one GC shank removed. You can see a minor tool mark on the left side but the boolits size to .311" nicely. Let me know if you'd like to see a pic of the aluminum MM which is a DC 195 grain PB. Click the thumbnail for a larger view. You can see I put a dab of cold blue on the bare metal after the mold was modified.

MJ

[Bret4207]

Just a thought, but check your runout. If the SWC starts a bit crooked, common sense tells me the higher velocity will accentuate any imbalance present. The SWC nose could contribute to the problem given the right circumstances.

[Marlin Junky]

Just a thought, but check your runout. If the SWC starts a bit crooked, common sense tells me the higher velocity will accentuate any imbalance present. The SWC nose could contribute to the problem given the right circumstances.

Bret,

Thanks for the post. I've already done that and I'm getting less runout with the Whelen using my dies and the 260 SWC than virtually anything else I load. I'm using ACWW metal which may be too soft for shooting beyond 1800 fps and I've got a marginal twist (I was thinking about hollow-pointing a few boolits to see if that makes a difference) and my accuracy really went to hell when I used a much harder lube than usual. Sure would have been nice to have pressure equipment hooked up to my barrel when I was testing the hard vs. soft lube. With a cold barrel the hard lube shot a 4.5", 5-shot group but a couple hours and 40 rounds later it shot a "nice" 3 inch vertical string (5 shots again). I used to estimate pressure by how much soot was on the case but I think that crude method flies out the window when shooting ACWW. FWIW, my cases were sooty all the way back to the pressure ring. I'm shooting boolits that are .0005" and .0015" over max. groove diameter.

Obviously there's several things I can try, but I'm doing the best I can w/o pressure equipment, software and time. Now, I need to hit the road again for the entire month of November. When I get back I'll probably stick with my softer, slicker lubes and heat treat a few boolits while sticking with my DP-74 (supposed to be 3% slower than AA2520) which seems to burn surprisingly clean at "low" pressure. I've already tried HT'd boolits and 49 grains of surplus H380 which produced pretty poor accuracy at 2100 fps which has prompted me to back off the velocity a couple hundred fps thinking the reason for poor accuracy may be the SWC boolit design going too fast. The chronograph stats with H380 weren't all that great but they can't justify the occasional 4" to 4.5" five shot groups at 75 yards.

MJ

[Marlin Junky]

I just thought of another variable that might be at work here... this particular rifle has a very long ball-seat which is .361" in diameter. I am seating my .3575" and .3585" boolits (max groove dia. is .3570") to touch the rifling but I think a harder alloy might be necessary.

MJ

[Larry Gibson]

Marlin Junky

Used to have that bullet, never did float my boat. Anything else?

Larry Gibson

[Marlin Junky]

Marlin Junky

Used to have that bullet, never did float my boat. Anything else?

Larry Gibson

Larry,

Most of my molds are .30 cal. Are you looking for plain base or gas checked?

MJ