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Is the micro-groove still made in 30-30 ? Are the as good as a normal barrel?
As William implies, Marlin still has Micro Groove barrels, and most shoot extremely well, even with cast bullets. In fact, I don't think I've ever seen a bad shooting Marlin, though rumour has it they exist.
 

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One thing to be wary of with Microgroove barrels is the frielapping with one of the graded firelapping kits on the market. I've heard of people using the 220 grit abrasive in these kits and damaging Microgroove rifling. You hear of the same thing happening with .22 barrels and smaller that have shallow grooves.

Marshal's kit from Beartooth Bullets with 320 grit abrasive is just fine for microgrooves. That's the same grade a lot of custom barrel makers use for hand lapping. If you already have a multi-grade kit, though, skip the 220 grit coarse grade and go straight to the next finer grit (400 in the two kits I'm familiar with) for Mircrogroove barrels and for .22's and smaller.
 

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As William implies, Marlin still has Micro Groove barrels, and most shoot extremely well, even with cast bullets. In fact, I don't think I've ever seen a bad shooting Marlin, though rumour has it they exist.
I have one. A 336RC built in 1957, given to me by a friend. Doesn't look like it's had more than a few hundred rounds through it, bore looks good, crown is fine, but after 5 or 6 shots it keyholes any 170 jacketed bullet I've tried. Clean it, and go through the same thing again. For those first few rounds, accuracy is fine - 1.5" to 2" @ 100 yds.

I thought the bore perhaps was loaded up with copper, but I've tried everything from JB compound to an Outers electrode system without curing the problem. 30-30 barrels are just about impossible to wear out through shooting, and I know that this rifle didn't see that kind of use.

First rifle I've ever encountered that had a mystery I couldn't solve. Frustrating.
 

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Do bullets shorter than the 170's keep flying true? Since it responds to cleaning, I'd slug it to feel for constrictions.
 
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Micro-Groove barrels have been the "normal" barrels for the 336 for 50+ years. They as as good as any, and better than many.
 

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Do bullets shorter than the 170's keep flying true? Since it responds to cleaning, I'd slug it to feel for constrictions.
That's a good theory. I've got a bore lapping kit that's got slugs for this bore, so I'll have to get around to doing that sometime.

I was going to rebarrel, but the work involved and the hassle of getting a barrel shipped to Canada killed that idea pretty quick.
 

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I have three. I been away from this forum for a while but guys here know what they are talking about. That barrel shoots true, keeping it from getting too dirty of course. I have a 39a, a 3030 and a win .375 all with that barrel. They all shoot an inch to one and a half. The thing I don't like is they (Marlin) don't handle dirt well for me. I can shoot one of my 94s all dirty and wet and no problems. Do the same with a Marlin and you get hang ups with ejection. But that should not matter because that first one goes where you point and that's that.
Mike
 
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