What Diameter Boolet For Micro-Groove

[alamogunr]

I just slugged the barrel on a Marlin 30AW(a 336 mfd for a mass retailer, I think). I've always heard that boolets should be sized larger for micro-groove. This one slugged .308. I'm thinking that .309-.310 would be OK. There wouldn't be much room for excess diameter to go. Comments?

[RickinTN]

Most of the advice I've read is to fill the throat. I shoot several Marlin 336's and shoot either .310 or .311 with pretty good accuracy. My rifles probably would take .312 but I don't have a mold that will cast that big. A poster on this forum (I'm sorry, I don't remember who to give proper credit) recommends "fat and hard" for Marlin micro-groove. Another yet (I think it is pls1911, but not sure) recommends "cast soft and heat treat hard" for micro-groove, and I think he sizes .312. Thus far I would agree with both of these members.
Good luck with your Marlin,
Rick

[alamogunr]

I should probably mike the boolet as cast to see where I'm starting from. I will also do a chamber cast to get an idea of the throat size. Hopefully there is one. My Swiss K31 has none at all. Just an abrupt transition to the rifling.

[jlchucker]

I think you need to slug the bore. Those Marlins are apt to be anywhere. I really lucked out when it came to 35 Remington and 45-70. When I bought my 45-70 I was new to handloading and even newer to cast boolits. I bought a .458 sizer based on what it said in an old Lyman manual about "most useful" diameters and got away with it. Same thing happened with 35 Remington. Maybe it was because I started loading those calibers for older guns, especially the 35's. Back then I hadn't gotten into reading very many gun magazines and hadn't heard about a so-called microgroove problem with cast bullets, either.

[alamogunr]

I did slug the bore(see OP). Measured .308. That would be the groove(such as it is) diameter.

[RickinTN]

The throats in my Marlin rifles measure .311+ and extend about .085 ahead of the case mouth. The leade in my rifles, except for one '49 model, is more a chamfer than a leade and is almost non-existant. The rifling starts very abruptly just ahead of the throat. I would be curious as to how yours measures.

[alamogunr]

It will probably be early next week before I can check the throat. I usually make what someone called an "impact throat casting".

Friday thru Sunday is pretty busy for me. I teach a class at church and this month I hold a devotional at a local nursing home before church. Not really very good at it but no one else wants to do it.

[bigted]

this is very easy to find the correct diameter for your rifle. unlike others i do not rely on the barrel meassurements except to see if the barrel is close to the expected dimensions.

instead what i observe as the best 'medicine' for all my rifles is what the fired case tells me. i first slightly flair the mouth so as to remove the previous crimp completely...now take a set of inside/outside calipers and incert the pointed section into the case mouth...now turn the case to just scrape off any fouling on the inside...now take meassurements in three places around the inside of your case...repeat with three fired cases fired in the rifle you want to get settup for.

this meassurement minus .001 inch is the diameter that will most likely perform best in a particular rifle.

now load 4 or 5 "dummy" rounds with this diameter boolit set to the correct length and see if they will work thru the action and chamber correctly...this is your boolit!

pay little attention to the bore or groove diameter unless you plan on shooting blackpowder...then all thoughts get different.

[jlchucker]

I did slug the bore(see OP). Measured .308. That would be the groove(such as it is) diameter.

I'd start with a few rounds at .310 and see what happens. You may not have to look any further than that. Good luck.

[popper]

311-170RF like the RD mould. I think NOE does this. 65111

[6pt-sika]

With the Marlin 30-30's I had be it Micro or Ballard I started with .309 later I went to .310 . Later yet I was trying to size some 311041 HP bullets and was bunmping them to much with the .310 mold so I went to .312 and they shot great . So after that all my bullets sized for the 30-30 guns be it Micro or Ballard were sized in a .312 die .

Worked for me , may or may not work for others .

[6pt-sika]

The Ranch Dog 311-165GC is an awesome bullet , I had one of the original test molds for this one !
I've shot probably 2,000 of these bullets in variouse Marlin 30-30's both ballard and Micro . Ran them ALL thru a .312 die and lubed with Thompson's Blue Angel .

This is an AWESOME lever silhouette bullet as well as a hunting bullet !

I had one of the original RD test molds for this jewel so got a bit of a head start . But air cooled wheelweights pushed with 20-22 grains of XMP5744 was a darned good load for knocking over the rams at 200 meters !

[imashooter2]

My 30AS slugs at .308 on the nose and I get best results with boolits sized .311.

[detox]

Lyman's 4th edition Cast Bullet Handbook states rifles with Micro-Groove rifling should keep velocities below 1600 fps for best accuracy. They also recommend a hard alloy like #2 or Linotype for best results. Recommended powders for 30-30 Winchester are Reloader #7, 5744, IMR 4198 (IMR 4198, 18 grains giving best accuracy @ 1602 fps). Manual also states rifle bullets using gas checks shoot more accurate. All boolits tested were sized to .308". Lyman's gas checked #311041 works verygood.

Purchase the LEE .308 sizer kit and see if that size works. If not ,you can hone the sizing die out larger using 600 grit sandpaper and dowel.

Tumble lube boolits in clear zip-loc baggie using warmed up Lee alox. To help mix alox, I put a lead boolit in bottle then shake.

[6pt-sika]

Lyman's 4th edition Cast Bullet Handbook states rifles with Micro-Groove rifling should keep velocities below 1600 fps for best accuracy. They also recommend a hard alloy like #2 or Linotype for best results. Recommended powders for 30-30 Winchester are Reloader #7, 5744, IMR 4198 (IMR 4198, 18 grains giving best accuracy @ 1602 fps). Manual also states rifle bullets using gas checks shoot more accurate. All boolits tested were sized to .308". Lyman's gas checked #311041 works verygood.

Tumble lube boolits in clear zip-loc baggie using warmed up Lee alox. To help mix alox, I put a lead boolit in bottle then shake.

Just because it's printed doesn't always mean it's correct !

My best accuracy with the RD 311-165GC and the 311041 and 311041 HP was about 1900-2100 FPS and again sized in a 312 die . Actually i don't think the 312 actually sized anything other then crimping the checks on .

I'll take what I saw for myself over whats printed in that book and yes I have a copy of it !

[TXGunNut]

I'm a big fan of the Lyman manual but IMHO they have some funny ideas about MG barrels, boolit diameter and hardness. I've learned from folks around here and thru my own experience that a fat boolit, properly dressed and lubed, does just fine in a MG bore. My 35 Rem RD boolits are sized @ .359 and are quite happy leaving the muzzle @ around 2100 fps. My 45-70 has had similar success at a slightly lower velocity-but well over 1600 fps. My HT boolits aren't even especially hard, generally around 15.
I'll try the 30-30 again someday and I feel confident a RD or a GB NOE 311-041 cast of 50-50, sized to .311 and dressed with a Hornady GC and LLA will get the job done, pretty sure it'll be more in the 2100 fps neighborhood, not 1600.

[451whitworth]

Lyman books always state the 1600fps level with the micro groove rifling. But if you look at their spec's (using the 30-30 as an example) they size to .308". A bullet sized to .311"-.312", whichever chambers, can be driven to full power jacketed bullet speeds no problem with equal accuracy. This is not new news as many people do it regularly.