Monthly Archives: October 2014

Overbore Addiction

Overbore Addiction

The Big .224’s

 

 

This is an overview on a subject that has been dubbed barrel burner cartridges. You know the talk “you’ll replace that barrel in 600 rounds, better have a good supply of extra barrels on hand, and the barrel makers will love you”.  As avid varmint shooters (that’s why you are reading this…right?) we all know about the effects of too much heat to a barrel will end up with an eroded throat, the 220 Swift was an example of this however shooters proved that otherwise with proper loading recipes and keeping barrel overheating in mind.

 

While shooting my 22-250 and 22BR I eventually became interested in the Big .224’s, sure I can push my 22-250 to 4000fps with 40grain woodchuck medicine but out to 500 yards bullets are taking the beating effects of wind and drift.  I had a copy of “Wildcat Cartridges Vol 1&2 by wolfe publishing” and became intrigued with the examples of .224’s pushing 80 grain bullets well into the 1000yard range.  These dedicated purpose cartridges are developed for long range shooting where long and heavy .224” bullets are used to buck the wind better and retain there energy out to extreme distances.  How this is done is sort of confusing to the reloader since fast twist barrels will most likely shoot best with fast burning powders and like wise for slow twist barrels and slow powder.  What I have found out is that to obtain the desired results from an Overbore case design is to load up with a slow burning powder, heavy bullets and a fast twist barrel.  The results are the longer the pressures push down those 26+ inch barrels enough velocity is produced to send the heavy .22 caliber bullets down range effectively.  Another factor that becomes apparent is the need to scrub out that bore more frequently (some as frequently as after 10 rounds) the high velocity produced in a small bore capacity tends to copper foul quicker and degrade accuracy.  A word of caution when working up loads is to always look for high pressure signs and stop shooting any load that produces such indicators.

 

There are numerous cartridges that fit this category and I will only just touch on a few.  Some need extensive case preparation and forming while others need only to be necked down, I consulted Quick Load for max case capacities, overflow grains in H2O and will list them from least to greatest:

 

 

 

 

  1. 22-250 A.I.           = 46.90
  2. 22-243                  = 50.00
  3. 22 Cheetah MK1  = 54.00
  4. 22 Cheetah MK II = 56.00
  5. 220 swift A.I.        = 57.00
  6. 22 Clark                = 59.00
  7. 22-284                   = 61.84

 

22-250 A.I.

 

Another P.O.Ackley success with his classic blown out case and 40 degree shoulder, velocities will push to 4000fps and has an effective range out to 500 yards. Reduced bolt thrust and case stretch along with the ability to chamber and shoot factory 22-250 loads make this extremely accurate round a versatile choice.

 

 

 

 

22-243

 

This cartridge was developed by Paul Middlested of San Diego, California it is based on the standard 243 Winchester case necked down to .224”.  The body dimensions remain unchanged only the shoulder angle is increased to 30 degrees giving a longer neck ( .300” vs .241” ), case forming is accomplished by running a 243 case thru a 22-243 full length sizing die. Velocities have been reported to exceed 4000fps while keeping groups well under ½ MOA @ 100yards, this cartridge excels with heaver bullets in the 68 to 75 grain range with rifling twist rates of 1-9 or 1-8. Other versions include the 22-243, 22-243 Middlested and 22-243 A.I.

 

 

 

22 Cheetah

 

The 22 Cheetah was developed by Jim Carmichel, shooting editor of outdoor life magazine and Fred Huntington of RCBS. The case is a full length Remington 308BR case with small primer pocket and necked down to .224”. There are actually two versions of this case one a MKI with a 40 degree shoulder and the MKII with a 28 degree shoulder. This cartridge has proven to be superbly accurate and very effective out to 300 yards.

 

 

 

220 Swift A.I.

 

P.O. Ackley’s Wildcat, blown out with a 40 degree shoulder. The three best known versions are the Ackley, Weatherby Rocket and the Kilburn, they share the mechanical advantage, extract better and cases last longer for the hand loader. Again better ballistics can be obtained over the standard case by the use of slow burning powder and heavy bullets.

 

 

 

 

 

 

224 Clark

 

Timothy Clark of Madera California designed this case for long range use around a flatter trajectory and harder hitting with greater retained bullet energy. The case is a 257 Roberts necked down to .224” with a steeper shoulder angle and expanded body, the 257 Roberts cases were found to be stronger as compared to reforming 6mm Remington brass. The small bore and relatively large case capacity and velocities ranging in 3800+fps to 4100fps can be a combination for short barrel life. Twist rates of 1-9 or 1-8 should be used to stabilize the long heavy bullets.

 

 

 

22-284

 

This variation of the 284 Winchester case is simply necked down to .224 (one way to accomplish this is with a 6mm-284 forming die then a 22-284 FL die) the 35 degree shoulder and body taper remain unchanged. We have arrived at the case capacity of diminishing returns where larger amounts of powder don’t necessarily result in greater percentages of increased velocity.  Accuracy will be best with heaver bullets as several conversations with gunsmiths have resulted in a preference of fast twist barrels and 70+ grain bullets. Reported velocities have been in the 3800fps range.

 

 

 

In closing there are several others not mentioned here such as the .224 Vais, and 22-6mm.  A look thru volumes 1 & 2 of Ackley’s Handbook for shooters and reloaders reveals quite a few and provides good insight on ballistics. Pressures can spike quickly with Overbores so a careful eye should be kept on spent cases along with sticky bolt lift. There is abundant information on these cartridges and with a little research you will be well informed on any specific cartridge. So if this small sampling finds you wanting more as it did for me grab your computer, some books and brew up a pot of coffee! Soon you will be chambering for that Overbore Addiction.

 

 

 

overbore 003

 

 

 

This is a handy chart I found on a cartridge forum posted from an unknown source. Interesting thou.

overbore table

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Mauser 22-250 Varminter Project

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Mauser 22-250 Varminter project

I’ve been shooting / reloading and buildings rifles for quite a few years and have realized the desire for small caliber varmint rifles. After a quick inventory of my battery of rifles, I noticed there was a M98 VZ24 Mauser action collecting dust. (Not really- just well oiled and tucked away.) After inspecting the receiver and bolt, the idea for a tack driving bench varmint rig was hot on its way. I decided on the 22-250 Rem. due to its classic accuracy and range. I have a small gunsmithing shop at my home, so the first stop was an order for forging blocks and heat sink to turn down that bolt handle. Following the grinding, filing and buffing, the bolt was ready for jewling. Then the Buehler low safety was installed along with a 26 lb. firing pin spring (Wolf). The bolt was finished and I was very happy with the end result.

Next, the receiver was checked for squareness and warp and the rear tang was tapered to give a sleek smooth approach for the bolt/stock fit. The receiver was then set in a jig, drilled and tapped for bases and the barrel threads chased with a standard 60-degree tap. Then the bolt lugs were lapped for a better fit with the receiver and the receiver rails polished for glass-smooth bolt push. I decided on a matt finish for the receiver so into the blasting cabinet it went. A heavy bead blasting resulted in a very nice finish for bluing and the results were pristine. An order was placed for an Adams and Bennett stainless steel bull barrel, .050 short chambered. Upon arrival, inspection proved to be excellent. Into the barrel vise for fitting to the receiver came next. Then I hand finished, reamed the chamber with a PTG finish piloted reamer, and checked for proper headspace with forster gauges. All the while this project was progressing, I had ordered a laminated stock from Richards Micro-Fit Stocks, marksman style in camo laminate.

It seemed like everyday I was eagerly opening a UPS package with more mauser varminter goodies inside. A Bold Premium trigger was fit to the receiver and I stayed with the factory heavy 2 lb-8 oz pull (just a starting point, you know) and a Leaupold one piece base was installed.

The trigger guard was modified for a sleeker look and finished to match the receiver. When the stock arrived, it was just what I wanted – a semi-inletted laminate with a slightly smaller barrel channel. Out came the rasps, files, bedding tools, and lots of sandpaper in varying grits. When I was happy with the shape and smoothness, pillar bedding was next. Then a steel rod bedded in the stock to help stiffen the recoil lug area. After reading several Gunsmith Kinks articles I decided to also bed the trigger guard along with the action. Pro Bed 2000 was the ticket for this task and it turned out as smooth a bedding job as ever! All the stock prep work was followed with a hand rubbed oil finish until a high gloss was attained. My next task was to make a custom fit steel butt plate that would display what I hoped would be what a varmint rifle should shoot. “MOA” was then placed on the butt plate and removed after sand blasting the piece. The bluing revealed a shinny logo stating “MOA”.
The end results of a VZ24 Mauser rebuild turned out to be one very nice looking bench shooting varmint rifle, weighting in at 10 lbs! A quick trip to my shop revealed a Leaupold VX1 4-12X40 scope on a 30.06 that didn’t see much use. So on the Mauser it went, along with Stony Point target knobs and bore sighting.

 

*ALL LOADS LISTED SHOULD BE REDUCED 10% AND WORKED UP SLOWLY, CHECKING FOR ANY HIGH PRESSURE SIGNS*

 

Factory ammo was purchased for seasoning the bore and much needed left over brass for the Forster Bench Rest dies to roll out some tack driving loads. The first day on the range proved to be a bitter cold February day around 20 degrees, but clear. After a proper settling in of the bore, factory ammo was grouping under one inch at 100yrds. Not bad for bulk Winchester ammo with that weird looking crimped tip on the bullets. No signs of headspace problems were evident so to the loading bench I went. Nosler Ballistic Tip 50 grn bullets were chosen along with the classic H380 powder at 37, 38, 39 grns to check for accuracy. The next trip to the range was warmer. The morning temperature was 40 degrees, clear with no wind. The best results were with the 37 grns of H380, which revealed a group of 0.338” for four shots with the fifth shot just outside of the ragged hole. I was very happy with the accuracy of my Mauser varminter! But accuracy is a thing of constant pursuit, so back to the loading bench to try different primers, however the overall cartridge length of 2.460” would be maintained. That placed the bullet ogive 0.030” from the rifling which proved to be a liking for this 26” 1 in 12 twist air gauged barrel. Case trim length of 1.90” would also be kept for uniformity.
The next trip to the range was windy and 55 degrees. The Winchester magnum primers proved to be a major step backwards with a five shot group opening up to a terrible 1.340”. A quick ammo change back to the large rifle primer loads proved a much better grouping at 0.400” (slightly larger than the previous results of 0.338”).

So after the range work was complete and several hours working up loads, my “MOA” Mauser was shooting SUB-MOA groups and I was pleased…until I pulled out the 55 grn bullets. The quest for accuracy continues! Did I mention that I also found a small ring Swedish Mauser action that I prepped the same way while doing the M98 action? Perhaps a Wildcat chambering would be a good choice. But that’s another story.

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