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Reaming a Marlin 336 to 30-30 Ackley Improved for Handloads

Not too long ago, Hornady’s ballisticians returned from a lengthy absence, shimmering with a divine afterglow, and bestowed lever action acolytes with the new gospel: LEVERevolution. After some initial skepticism and confusion (gimmick? God’s gift?), it didn’t take too long for the .30-30 faithful, in particular, to realize they were living in sweet times.

But long before LEVERevolution happened to the .30-30 Winchester, Parker Otto Ackley happened. The .30-30 Winchester responded to the famous gunsmith’s touch like few other cartridges. Blowing out the body taper, and sharpening the shoulder of the world’s first commercial smokeless powder cartridge yielded remarkable gains in performance. In addition to an increase in case capacity and efficiency, the new shape gave the case the ability to handle sharply increased chamber pressures. As a result, this perennial wildcat regularly gets pushed to velocities far higher than it’s small capacity increase would suggest are possible.

What kind of performance increase can one expect with the .30-.30 Ackley Improved? That friends is a matter of some debate. Actually, more than some debate. A lot of debate. As in decades worth, since P.O. Ackley himself started it. But for those of you contemplating the 30-30 A.I. modification to rechamber your barrel, here a few things that I can say about it with reasonable certainty:

1) The “Improvement” is decidedly a benefit only to the hand loader. Factory Win .30-.30 ammo can be fired in the chamber safely and accurately, but there will be a small decrease in velocity due to the larger expansion area in the chamber. The benefits can only be reaped by reloading fire formed cases to their higher capacity.

2) Velocity gains of at least 100fps with all bullet weights are a well established safe expectation that will keep chamber pressures close to standard. The .30-30 AI has been widely experimented with in Marlin lever action rifles, and while many of those experiments have been well documented, to my knowledge no ammunition or gun manufacturer has published load/pressure data for the cartridge. If one wishes to push beyond chamber pressure limits established for the standard .30-30 (and many have), he is well advised to use prudence and due diligence to guide his efforts.

3) IMPORTANT! Because the less tapered case walls of the .30-.30 AI dramatically reduce bolt thrust, one cannot rely on normal over-pressure signs (e.g. flattened primers or sticky extraction) to appear before chamber pressures reach a level that may be unsafe in the host rifle. Avail yourself of the wealth of research already done, including by Ackley, and proceed with caution and restraint.

If all of that sounds fairly uninspiring, then why make the change at all? There actually are some pretty good reasons.

1) SAVE MONEY - If you love your old .30-30 lever gun, but have been furtively looking at, say, a new Marlin 308 Express, you might consider the Ackley Improved chamber as a cheaper alternative. For one thing, if you’re like me, you probably have plenty of .30-30 donor brass laying around, which means you don’t have to make another investment in new brass or factory ammo. That by itself represents a significant cost savings.

2) MORE POWER - In reality, handloaders have been using the .30-.30 AI for decades to get most of the performance of the .308MX. Velocities of 2500-2600fps with 150gr bullets are recorded all the time. As far as I know, folks aren't blowing themselves up in droves either. Again, caution and prudence. If you need more power than the Ackley can safely offer, just buy another gun. Attempts to overtake modern cartridge performance may end in disaster.

3) INCREASED PRECISION - While there is no guarantee of enhanced accuracy in the newly improved chamber, many have reported increased precision. Take a look at what happened with our recent experiment:

Since my own experience with the .30-.30 AI chamber was limited, I wanted to play around with our new PTG Chamber Reamer so I could offer our customers the benefit of more first hand experience. I selected a pre-safety Marlin 336 from our stock that was in good condition, with an excellent bore, which I scrubbed before heading to the range. Using a Hodgdon Varget handload that typically shoots well in Marlin 336’s, this test rifle delivered a disheartening 3.5” group at 100yds, with 8 shots scattered mostly at random. We rarely encounter such piss-poor performance in Marlin rifles, but when we do, those rifles are treated as suspect so as not to become RPP custom rifles.

Nonetheless, I figured that if we couldn’t improve the barrel, it would become scrap anyway, so I went ahead and reamed the chamber, making a couple of accurizing tweaks along the way. Then, I once again scrubbed the bore and went to the range. With the same Varget handloads as before, I fired one sighting shot at 100yds, the recoil impulse feeling milder than ever. After adjusting the scope, I fired one of the tightest 3-shot clovers I’ve ever seen from a Marlin 336 at just over ¼”. Two more subsequent shots opened that amazing group to just over one inch, but the rifle had clearly turned a corner. Two more 4-shot groups using AI formed brass and max .30-30 loads proved this, each printing a minute of angle (MOA) at 100yds.

I decided it was time to do some more in depth testing, so new, warmer loads were made up, and we set up our Chrony to record muzzle velocities at our private test facility. Once again, the Marlin 336 test rifle printed a succession of tight groups, both with our handloads and with factory LEVERevolution. With the latter, velocity fell off about 70fps in the improved chamber, alongside a second factory Marlin 336 that recorded consistent velocities of 2330fps. Our warmest 30-30 AI handload, packing 36.5gr of LVR behind the 160 FTX bullet, turned in velocities 100fps in excess of our factory control Marlin 336 rifle. Incidentally, that load is only 1.0gr in excess of Hodgdon's listed max for the .30-30, and still .5gr lighter than Hornady's listed max for the same bullet/powder combo. Probably a safe bet.

The Marlin 336 rifle was shooting so well that after running out of 30-30 AI handloads, and despite gusty conditions, I decided to send a few Hornady FTX factory rounds out to the 200yd target. From a fairly warm barrel, the first 2 rounds went so tightly through the same hole that I had trouble distinguishing them through our quality spotting scope. A fluke? Probably, but 2 subsequent rounds kept the group handily under MOA. At this point I stopped, feeling that there was little to be gained from going to the 300yd target in gusty conditions with the soft shooting factory loads.

It’s worth noting that our test Marlin 336 rifle wore a simple Nikon 3-9x scope without adjustable objective, and the rifle itself lacked any of the niceties, like a cheek rest, that bolt action target rifles are normally afforded. There is a possibility too, that further accurizing work might reduce group size consistently to sub-MOA. In any case, I feel that with careful load development, the Marlin 336 rifle can be a legitimate tool for harvesting deer at ranges in excess of 300yds, should a hunter possess the requisite skill and judgment.

So, what does all of this prove? Scientifically, it proves nothing. Obviously the test parameters are too limited. But it does illustrate the intriguing possibilities that P.O. Ackley tapped into.

We charge $100 to ream a Marlin .30-30 chamber to Ackley Improved spec. That is less than a quality chamber reamer costs these days, and a fraction of the cost of a new rifle. We ream the barrel with great care to give you a chamber that is true, chatter free, highly finished, and properly head spaced. As part of that cost, we address feed issues, which often arise with the new, less tapered cartridge, and will modify your magazine follower for improved function with FTX bullets. Accurizing tweaks are an additional charge, but the end result may be that you own a Marlin 336 rifle that delivers most of the performance, and possibly better precision, than a new Marlin 308MX rifle. Then again, if you like buying new guns as much as I do, you can always do both…

- Adam Devine

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