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>> .444 Marlin- America's Most Versatile Big-Bore Part II :: By Marshall Stanton on 2001-07-12
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Part II Barrel dimensions, condition and bullet fit.

In the previous section we looked at the Marlin 444S and it's shorter barreled counterpart the .444P "Outfitter" models both chambered for the .444 Marlin. In continuing our look at the .444 Marlin- America's Most Versatile Big Bore, this segment will focus on barrel condition, dimensions and bullet fit for optimum performance in these rifles.

As mentioned in Part I, the .444 Marlin has garnered an undeserved reputation for being a poor to lousy shooter of cast bullets at anything over .44 Magnum velocities. This unfortunate misconception stems from a lack of understanding of bullet fit and barrel dimensions. Couple poor bullet fit with soft bullets lacking strong front driving bands along with the notoriously rough bores of Marlin's Micro Groove Barrels, and indeed you have a perfect recipe for unsurpassed cast bullet failure!

First let us look at those Marlin Barrels. The chambers in both the Micro Groove models as well as the newer Ballard style rifled guns have chambers with fairly generous proportions in the throat area of the chamber. Typically the throats, while being fairly short, are larger than most folks expect, with the diameter running .4325"-.433" on the average in most guns. For best results using cast bullets, that large throat diameter needs to be filled up for best performance, facilitating bullet alignment with the bore prior to ignition of the cartridge. An undersize bullet has the propensity to yaw or tip in the throat before engaging the lands of the rifling, thus causing the projectile to enter the bore off-center.

As mentioned earlier, the Micro-Groove barrels very typically have a generous helping of machine marks in the bore which, for best cast bullet shooting need to be lapped to some degree. Fire lapping is the easiest and most efficient way to deal with this aspect of bore preparation. (Complete instructions for fire lapping are contained in The Beartooth Bullets Technical Manual. Click here for more information!) While the new Ballard style rifled barrels have bores of a much better condition in regard to machine marks, they too need lapping for best results when shooting cast bullets.

Why do those nice new Ballard barrels need to be lapped? Because of constrictions in the bore! Both the Micro-Groove models as well as the new Ballard style rifled barrels have constrictions in them. These constrictions are located under the dovetail cut on the underside of the barrel for the magazine tube hanger, under the dovetail cut for the rear sight and again under the roll-stamp engraving of the barrel markings on the left side at the rear of the barrel. While the severity of constriction varies from one gun to another, they are there none-the-less on all of these big bore rifles (both .444 and .45-70).

Of the two guns used for testing in this article, the Micro-Grooved .444S model rifle was fire-lapped over fifteen years ago, relieving the barrel of not only the bulk of the machining marks in the bore, but all traces of constriction in the locations mentioned above. However, the Marlin .444P "Outfitter" model used for testing in this series had not been lapped, and had seen only cast bullet use. Using a number eight oval egg sinker (see our FAQ pages for instructions on slugging, or Beartooth Bullets Technical Guide for complete instructions. Egg sinkers available click here.) we slugged the barrel of the new .444P. Actually we used several sinkers, and slugged just the muzzle, then drove a sinker as far as the forward dovetail for the magazine tube hanger, then removed it to measure the constriction at that point, then repeated the process from the breach end shoving the egg sinker as far as the rear-sight dovetail and once again removed the slug to determine extent of constriction under the sight dovetail. Finally we inserted another egg sinker and shoved it to the central point under the roll-engraving of the barrel markings at the left rear of the barrel. From the measurements obtained from each of these slugs, the amount and location of the constrictions in the barrel were determined as illustrated below.

Once determined that there was a full .002" constriction as well as a .0015" constriction in the bore, firelapping was the next step before any serious load development could commence. However, in the interest of illustration, we loaded a proven combination used in other .444's, for before and after accuracy testing. Although the load was not worked up to obtain best accuracy with the .444P in its pre-lapped state, the load has proven itself very accurate in other .444's. Twenty rounds were loaded in one session, ten being expended shooting two groups of five before fire-lapping, and the remaining ten after the lapping process was completed, once again in two five shot groups.

In preparation for load development and accuracy testing, the Ashley Ghost Ring rear sight was removed, and a Weaver scope base mounted, along with a 4x scope for shooting groups. The addition of the scope was done before shooting the groups fired prior to fire-lapping. Both rifles used in load development for this series of articles will wear glass optics throughout the load testing portions of these tests.

Lapping loads were prepared in accordance with the instructions found in the Beartooth Bullets Technical Guide, and loaded with 5.5 grains of Bullseye for a lapping charge using Winchester Large Rifle Primers for ignition. Forty-seven lap loads were fired in sequences of five round volleys, slugging between sequences, feeling for constriction reduction. Finally at forty-five rounds, little or no constriction could be felt throughout the bore, two final rounds were fired, and once again the bore was slugged, and all traces of constriction were gone. At this point a polishing bob was prepared and 200 strokes were given to the bore as a final polish, and the bore broken-in with a conventional break-in sequence before shooting for groups.

Interestingly, the point of impact at 100 yards raised over 5" after fire-lapping when compared to pre-lapping sight adjustment. Typically I chronograph my test load both before and after lapping, but failed to do so on this rifle. My hunch is that the barrel gained some velocity due to a reduction of friction coefficient in the barrel after fire-lapping, thus explaining the elevated point of impact, but since I didn't chronograph the loads prior to lapping, this is of course pure speculation. It might be interesting to note that this is the most significant change in point of impact I have ever encountered by simply fire-lapping a barrel. Once the post-lapping break-in process was complete, the gun shot remarkably tighter groups when compared to those fired before lapping. Keep in mind that this ammo was not developed specifically for this rifle, and that all twenty rounds were loaded on the same press, with the same setting on the powder measure, at the same loading session. They were all fired on the same day, from the same bench, on the same range by the same person. The only difference is that two groups were fired prior to lapping, and two fired post-lapping and break-in. The ambient temperature rose one degree between the initial two groups and the final two groups.

Test Load For .444P "Outfitter" .444 Marlin: 
.432"-325g WLNGC/56.0g H335/WLRP/Rem Brass/C.O.L. 2.570"

Test Prior To Fire Lapping

Group I

100 yards

87 Degrees Fahrenheit  2.970" Group Center to Center
Group II

100 Yards

87 Degrees Fahrenheit 2.282" Group Center to Center

Test After Fire Lapping and Barrel Break-In Procedure

Group III

100 Yards

88 Degrees Fahrenheit 1.186" Group Center to Center
Group IV

100 Yards

88 Degrees Fahrenheit 1.159" Group Center to Center

With both test rifles having bores free of constrictions and being equally prepared in terms of scopes and bore conditioning, it is fitting that before doing any serious, meaningful load work-ups that we explore bullet diameters and barrel dimension relationships and how they apply to accuracy and cartridge performance. In slugging both guns we found that the groove diameter of the Micro-Grooved barrel of the .444S measured .4315", and the Ballard Rifled barrel of the .444P had a groove diameter of .4305".

To determine the effect of bullet sizing diameter, we selected the same 44 caliber 325 grain WLNGC bullet as used in the before and after lapping group shooting heat-treated to a BHN 21 and sized to various diameters listed in the table below. All load components remained the same throughout the tests, for the sole exception of the bullet sizing diameter. All groups were fired at 100 yards from the Beartooth Bullets Shop Range off of sandbags and are the average of two five shot groups measured center-to-center for each bullet diameter, for each gun. The results speak for themselves.

Test Load For .444 Marlin:
.44 Caliber 325g WLNGC/56.0g H335/WLRP/Remington Brass/C.O.L. 2.570"

Bullet Sizing Diameter Group Size Marlin 444S (Micro-Groove) Group Size Marlin 444P (Ballard Cut Rifling)
.428" 4.64" 4.28"
.429" 4.26" 3.97"
.430" 3.56" 3.34"
.431" 2.18" 1.87"
.432" 1.22" 1.17"

After examining the results of this test, .432" diameter bullets are the clear choice for use in the .444 Marlin when dealing with cast bullets. Those bullets of smaller diameter will deliver the typical, stereotyped performance that have given Marlin center-fire rifles a bad reputation for cast bullet shooting! Note too that those bullets smaller than .431" left significant lead deposits in the bore, more so in the Micro-Groove barrel of the 444S, and the amount of lead in the bore increased as bullet diameter decreased below .431".

Now, having relieved the constrictions in the barrels of our test rifles, and determined optimum bullet sizing diameter, we are prepared to enter into some serious load development in Part III of .444 Marlin- America's Most Versatile Big-Bore.

.444 Marlin- America's Most Versitile Big-Bore Part I | .444 Marlin- America's Most Versitile Big-Bore Part III

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