RCBS 308-SIL Molds

[Boomer Mikey]

I've been an RCBS guy all of my reloading life which began in the early 1980's; I believe it was somewhere around 1982 that I started making handloads for IHMSA competition and my life long shooting buddy and mentor J.D. said that if the equipment wasn't green and the brand name didn't start with an "R" I was wasting my time and money... J.D. has always been a reliable source of no B.S. accurate information and I would never doubt his recommendations but over the years I've added excellent products from other manufacturers to the loading bench and workshop in blue, red and orange colors too.

When the "cast your own" bug struck in the late 80’s I naturally purchased RCBS casting equipment and molds. Some of the first molds purchased were the 7mm and 30cal SIL series molds, 35 and 44 molds soon followed as well as 6mm, 270, and 45 caliber models.

I presently own so many molds I can't remember what and how many there are but apparently I've become a mold collector as I have 6 drawers full of them and until recently the 30 cal drawer only contained RCBS 130 SP, 150CM, 150-FN, 165-SIL, 180-FN and 180-SP molds. Since I found this place (cast boolits) last year I’ve collected Lyman 311041’s, Saeco 315’s, and numerous Custom 6 cavity Lee group buy molds.

Over the years I’ve relied on the RCBS 165-SIL and 180-SP molds for all of my very limited 30 Herrett, 308 and 30-06 work. The old 165 has a 0.301" nose and 0.310" body, the 180 had a 0.302" nose and 0.311" body. I liked the design of the 165 over the 180 because the 180 left a lube groove exposed and in some applications the bullet required seating deep in the case leaving lube exposed to powder. I’ve never been satisfied with my results using the 165-SIL and until this last year I thought it wasn’t possible to do much better than 3” 100 yard groups and there was always another project to work on.

BruceB’s work with the M1A lit a fire within me so I ordered a “Loaded” model and started work on cast loads for the M1A and a Savage 10FCM scout rifle; after going through all my cast 30 cal bullet inventory with a Stony Point OAL gage as a guide only the RCBS 308-165-SIL and 308-180-SP designs as well as the 165-SIL modified GB design seemed appropriate for my needs. The 165-SIL was suitable for use in the M1A and Scout and the 180 was fine for the Scout as well. I insist that M1A loads function reliably without feeding or extraction issues; the Modified 165 SIL GB boolits chamber too hard into the lands to be reliable and the 180’s wouldn’t seat in the case neck at a location suitable to apply a taper crimp to prevent bullet movement. This left me with one bullet for the M1A that has an undersize bore riding nose at 2.7” COL and 3” groups @ 50 yards.

Options:
Beagle the 165-SIL mold… boolit’s nose is now too large to chamber.
Apply molly mold release to GB mold cavities to reduce nose as cast diameter… undesirable.
Seat GB mold bullets deeper… expose lube to powder.
Find another bullet/mold that drops bullets that fit better… the RCBS 308-200-SIL, a similar design to the 308-165-SIL.

Midwayusa had the 165-SIL available with a price reduction when I ordered the 30-200-SIL so I ordered another one. I was surprised to find the new 165 mold produced slightly heavier bullets with a 0.302" nose and 0.311" body and a slightly larger meplate. The new mold’s bullets are a perfect fit in both rifles with the nose seating uniformly into throats of both rifles at 2.7” COL in 308 brass.

The 308-200-SIL nose tapers from 0.299" to 0.308" at the first drive band with a 0.310” body. COL in 308 brass is 2.850 (max reliable feed length in my M1A). The bullet seating length range engraves the rifling perfectly in both rifles with no extraction/feed issues.

Both of the new molds cast beautiful boolits without any release issues.
Alloy 50/50 WW/Linotype WQ:
Naked weights.
Old 165 167 grains
New 165 169 grains
200-SIL 201 grains

I’m looking forward to the next range session.

Boomer

[45 2.1]

The Modified 165 SIL GB boolits chamber too hard into the lands to be reliable

Midwayusa had the 165-SIL available with a price reduction when I ordered the 30-200-SIL so I ordered another one. I was surprised to find the new 165 mold produced slightly heavier bullets with a 0.302" nose and 0.311" body and a slightly larger meplate.
The GB mold was supposed to have a tapered front of 0.300" to 0.302" for the front part of the nose behind the meplat radius. The bands were supposed to be 0.312". I would be interested in knowing what your mold produced with the alloy you listed below and just where it engauged when you tried it.

The new mold’s bullets are a perfect fit in both rifles with the nose seating uniformly into throats of both rifles at 2.7” COL in 308 brass. I've been useing a slightly larger cut of the GB boolit in some Cetmes and M1As with no problems. I would think that after you shoot that new rifle for awhile, you will find that the GB will engauge properly after the throat gets wore some. Give it some time and try it.

Alloy 50/50 WW/Linotype WQ:

[Boomer Mikey]

The GB mold was supposed to have a tapered front of 0.300" to 0.302" for the front part of the nose behind the meplat radius. The bands were supposed to be 0.312". I would be interested in knowing what your mold produced with the alloy you listed below and just where it engauged when you tried it.

I've been useing a slightly larger cut of the GB boolit in some Cetmes and M1As with no problems. I would think that after you shoot that new rifle for awhile, you will find that the GB will engauge properly after the throat gets wore some. Give it some time and try it.

The problem with my Modified SIL GB mold isn't one of design; it’s one with Lee's manufacturing tolerances. Bullets dropped from this mold are out of round (offset blocks) by 0.001" and there are cavity variations of up to +0.001”. Indeed, the nose does taper from 0.300" - 0.302" perpendicular to the parting line. Depending on where the GB bullet lands in relation to the grooves and lands determines whether the bullet seats too hard or not. I found some instances where it was necessary to push the op rod forward to lock the bolt.

Yes the rifle is new; the throat may be a little rough, and with more bullets down the bore the GB bullets may work fine but for now the bullets from these new RCBS molds makes their use in the M1A a no-brainer. I’m sure if I were to sort my GB mold bullets by nose diameter where they engage the throat they would work fine… I’m too lazy to do that and I’m not going to tempt fate by pulling the trigger on an M1A with an unlocked bolt.

Bore riding bullets may require a higher level of precision and quality than some designs to work well in some applications. A custom sizing die could be made to make my GB mold bullets noses uniform in size and I would bet that doing so would result in improved reliability and ballistics but IMO not worth the effort for this application.

Boomer

[rvpilot76]

Boomer:

I too am on a quest with the RCBS 200 SIL in my M1A. I am concerned, however, that the use of heavy boolits in this rifle will harm it. I have read that boolit weight should not exceed 180 grains in the M1A. Obviously, we are not going to be setting the world on fire, as far as velocity goes, with these heavies. Would you mind sharing your load recipe with the 200 grainer in your M1A? I am thinking that a low starting J-Word load would be about right for our heavy cast use. I've also read somewhere that the use of slow-burning powders, ala 4831, is a no-no in the M1A. I'll probably start with Varget and RL15; I've also got some Benchmark I'll probably give a shot as well. I'm just going to stay in the medium burn rate area, so that the action will still cycle, so no shotgun powders.

Kevin

[Boomer Mikey]

Boomer:

I too am on a quest with the RCBS 200 SIL in my M1A. I am concerned, however, that the use of heavy boolits in this rifle will harm it. I have read that boolit weight should not exceed 180 grains in the M1A. Obviously, we are not going to be setting the world on fire, as far as velocity goes, with these heavies. Would you mind sharing your load recipe with the 200 grainer in your M1A? I am thinking that a low starting J-Word load would be about right for our heavy cast use. I've also read somewhere that the use of slow-burning powders, ala 4831, is a no-no in the M1A. I'll probably start with Varget and RL15; I've also got some Benchmark I'll probably give a shot as well. I'm just going to stay in the medium burn rate area, so that the action will still cycle, so no shotgun powders.

Kevin

You've got the right idea; The worry with heavy bullets is bending the op-rod and hammering the bolt into the action with high pressures in the gas system that you won't reach without destroying cast bullet accuracy. The rifle will make a "clip clop" sound when things are working well.

My favorites at this time are XMR4350 and Accurate 2520. H4895 and Accurate 2460 are also promising. 2520 is similar to 4064 and 2460 is similar to H335. For some reason H4831 doesn't cycle my action reliably but it's accuracy is good and you can't get enough in a case to reach maximum pressure. I'm not the expert, but I'm reducing 308 rifle load data, using 308 Federal brass (thick necks) and keeping pressures between 30,000 and 40,000 PSI with BHN 21 bullets.

My results are inconclusive... a work in progress; it would be inappropriate for me to list load data at this time.

Remember your 7.62x51 NATO M1A has a 55,000 PSI maximum pressure rating compared to the 308's 60,000 PSI. Adjust loads accordingly between 308 brass (larger capacity) and NATO brass (less capacity).

Get yourself a Redding 308 taper crimp die to eliminate case neck flare and provide bullet pull resistance for better ignition.

The M1A is prone to slam firing if you don't seat primers below the case rim and CCI primers will reduce the probability of a slam fire with it's stronger cup.

My LBT Blue lube is soooo good that my gas system got gunk-ed up in less than 100 rounds. BruceB's notes say his gas system didn't have any problems using felix lube.

As always, confirm load data with a reliable source... your practices and procedures may differ from mine and our rifles may be considerably different.

Boomer

[Larry Gibson]

rvpilot76 and boomer

"I am concerned, however, that the use of heavy boolits in this rifle will harm it. I have read that boolit weight should not exceed 180 grains in the M1A."

It is the M1 Garand that one should use this caution with. The M1A has a completely different gas system. The gas cylinder cuts the pressure off at a certain level. You will not bend the oprod with bullets over 180 gr. I have shot many, many 311299s at 205 grs out of my M1As and a couple M14s without problem. I settled on 4895 and accepted a velocity of 2100 fps as being the max before accuracy started going south. That was 137,400 RPM out of the 11" twist of my Fulton Super Match M1A. I shot a few 200 yard reduced NMCs with that load and had high Expert scores. I averaged about 5-8% less points with the cast load vs with J match bullets. Good enough for practice matches. On Accuracy was not quite as good out of the 12" twist Match M14s. My 311041HP gave the best accuracy in the M14s at 1900 fps. The scores with the M14 were as good as with the Fulton Match. I probably could have slowed the 311299s down and gotten better accuracy but I never got around to it.

The 165 SIL bullet should be a good one for the M1A. I wouldn't worry about the pressure difference between the 7.62 NATO and .308 winchester as you will lose accuracy way before you reach max pressures. The max pressures are the same for both cartridges BTW. SAAMI pressures for the .308 are most often quoted as maximum allowable pressure and pressures for the 7.62 are average working pressures. Also most current industry psi measurement (not to be confused with CUP psi measurements) for the .308 are taken with conformal transducers placed over the case body. All 7.62 NATO pressure testing is done with a casemouth transducer. The case mouth transducer gives a lower psi than the conformal transducer. We must also remember that just because the max psi is listed at 60 psi doesn't mean all ammuntion is loaded to that. Quite the contrary. In actual pressure measurement of numerous lots of U.S. M80, M852 and M118 Special Ball along with numerous different makes of .308 Winchester commercial ammo I find that the 7.62 NATO ammo is usually 3-5,000 psi less that commercial .308 Winchester.

For what its worth; I also have obtained the test pressure from the manufacturers of several different lots of .308 Winchester ammo to use as "reference" ammo as comparison to psi readings with my Oehler M43. The pressures mesured at 70 degrees were slightly higher in my 10" twist barrel and slightly lower in the 12" twist M70. The 10" twist barrel has less than 600 rounds through it and the 12" twist has almost 3,000. In neither case did the pressure vary more than 2,000 psi form the report factory psi for any lot. From what I'm told by several ballasticians who measure such this is a quite consistant reading from the M43.

Larry Gibson

[Bob S]

Chamber pressure requirements for A130 (the Army calls it M80 Ball) from the Mil Spec, shows the difference between the two common measurement methods:



And port pressure requirements:



You can still get into trouble with excessive port pressure in an M14, but it it is far less likely than with an M1.

The old USMC G3 (long range) load had a port pressure in excess of the specified values and required the gas cylinder lock screw to be vented, in addition to the "stock" gas cylinder vent.

Resp'y,
Bob S.