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Hi MarlinOwners Forum Members - Interested in reaming your Marlin 336 to 30-30 Ackley Improved for handloads? Here is my experience and some tips that might help you. Best Adam.

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.

30-30-Ackley-Improved.jpg
 

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.30-30 AI Chamber is Planned for the Next Mod. on my "Custom, Marlin Inproved, Tree Stand Gun"
Already has 17.5in Barrel w/ Recessed Crown & Button Mag.
Already Shoots Cast 170gr RNFP Exceptionally Well w/ 28gr IMR-3031.
With the AI Chamber I Plan to Explore Possibilities w/ LVR & Higher Velocities.
UncleSarge58
 

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Hi MarlinOwners Forum Members - Interested in reaming your Marlin 336 to 30-30 Ackley Improved for handloads?

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.

View attachment 106855
Very cool post, thanks for writing it up like that.

How do you form the brass? And what accurizing tweaks did you perform?

Finally, how much would this process cost?

Thanks,

Brocky
 
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Discussion Starter #4
Very cool post, thanks for writing it up like that.

How do you form the brass? And what accurizing tweaks did you perform?

Finally, how much would this process cost?

Thanks,

Brocky
Brocky,

AI brass is formed simply by shooting .30-30 cartridges in the improved chamber. Then an AI sizer die is used when reloading. Pretty simple.

On this particular rifle I did little in the way of accurizing tweaks since I wanted to focus more on what "improvements" the new chamber might offer. I did eliminate a point of contact between mag tube and barrel just behind the muzzle. Otherwise a little trigger work, and that was it. On our custom builds the accurizing is much more extensive. I'll be posting a blog on our website on that topic soon if you want to learn more.

We charge $100 to do the AI conversion, which includes reaming the chamber, sorting out feed issues which often arise as a result of the new case profile, and modifying steel followers to work more reliably with FTX bullets.

Best,

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I'll be posting a blog on our website on that topic soon if you want to learn more.

We charge $100 to do the AI conversion, which includes reaming the chamber, sorting out feed issues which often arise as a result of the new case profile, and modifying steel followers to work more reliably with FTX bullets.
Very cool. I'll be checking that out.

Thank you!

Brocky
 

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Anyone Have a .30-30 AI Reamer?

Anyone Here on M.O. Have a .30-30 AI Reamer that they'd be Willing to Loan or Rent Out?
Sure would Like to Rechamber my Lil' Treestand Gun & Give it a Whirl.
I have Found a Place On Line that I can Rent One from:
30-30 Ackley Floating Pilot Chamber Reamer
Just in case Anyone (Besides Me) is Interested.
Just Figured I'd Try Here First.
If Someone Does, Please PM Me.
UncleSarge58
 
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Discussion Starter #7
Sorry Sarge. As much as I would like to help out, we career mechanics have a hard-learned and deep seated anxiety when it comes to loaning out tools. Most of us learn early on that the potential downside (which has nothing to do with loss of profit) outweighs the opportunity to foster goodwill. I hope you won't take offense.

I haven't tried a rental reamer yet, but I haven't read anything bad about their system. Might be worth a shot.

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