level of accuracy is expected, their use of a tighter chamber on their sporting rifles prevents the use of Stinger and similar sporting ammunition. When a shooter tries to use Stinger ammunition in these rifles, the round tends to become stuck in the chamber well before the bolt can be fully closed. For some semi-automatics chambered with the “Bentz”
chamber, a chamber significantly tighter than the standard SAAMI sporting chamber, the spring force of the recoil system will not have enough energy to mash the bullet into the chamber far enough for the bolt to fully close, creating a jam-o-matic out of a semiauto. The photo below shows the differences among chamber
dimensions when a Stinger round is inserted. At the top of the photo is a barrel chambered with a Pacific Tool & Gauge (PT&G) ECX match reamer. Almost half of the round still hangs out the end of the chamber, yet the bullet has already become stuck against the chamber walls. The barrel second from the top is chambered with the PT&G Eley #5 match reamer. While the Stinger was able to fit a little deeper inside, it still has quite a ways to go before the bolt can be closed. The third from the top barrel was chambered using the same method for the two Lilja test barrels in this article. The reamer used was a PT&G SAAMI Sporting reamer, but not run to its max depth. I stopped just short to allow the bullet to engage the leade angle as the bolt closes. The final barrel at the bottom is from a semiautomatic rifle and chambered with the same PT&G SAAMI Sporting reamer, but run to its full depth. Here you can see the case rim sits on the breech face, allowing the bolt to fully close. TESTING EQUIPMENT
I selected three rifles in order to evaluate the Stinger’s accuracy, velocity, and field performance. For accuracy and
velocity testing, I used my Unlimited test rifle – an Anschutz 2013 receiver and trigger, Shehane stock and a Leger return- to-battery one-piece rest. Topping the rifle is a Leupold fixed 35x BR scope. It’s a beast of a rifle in terms of weight, and having shot this setup for a number of years, it has proven both accurate and reliable. Switching barrels is easy since it’s a clamped tenon, with the front part of the action free-floated to avoid binding in the bedding when barrels are switched. The second rifle was another Anschutz 2013, fitted
with a three-position target stock and a Leupold/Premier 18x40x40 silhouette scope. I used this rifle because it can share barrels with the other 2013 and it’s quite enjoyable to shoot both at the range and out in the field, even in spite of its considerable weight. The third rifle was a Tactical Solutions X-Ring semi-
auto fitted with a 16.5" aluminum-sleeved Chromoly barrel and Cascade Monocore suppressor. On top of this rifle was another Leupold scope: the EFR 6.5x20x40mm. The EFR is great for shooting targets close in and still having a high- level of magnification. A fiberglass Bell & Carlson stock completes the rifle and makes for a nice, lightweight, and quiet varmint hunter. Three barrels were selected for this project: one Lilja
27" heavy barrel, one Lilja 18" heavy barrel, and one factory Tactical Solutions aluminum-sleeved Chromoly barrel. The two Lilja barrels were chambered with a PT&G SAAMI Sport- ing reamer and did not feature any tuning device. I ran the reamer in just deep enough to allow the Stinger’s driving band to slightly engrave the lands when the bolt is closed. It is not so tight that it required excessive force to cam over the bolt handle, but snug like a benchrest rifle with match ammunition. The Tactical Solutions barrel was chambered with a similar reamer from PT&G, but run to the full depth during production at their facility. RESULTS WITH THE STINGER
For testing, I had two bricks (1,000 rounds) of ammu-
nition direct from CCI to work with. The Stinger’s accuracy was based on shooting ten 10-shot groups at 50 yards with the unlimited rifle riding in the one-piece rest. Using stan- dard benchrest rifle handling techniques including a sturdy concrete bench and a series of wind flags, the groups were shot from a clean barrel with one 15-shot fouling group to precede any groups for measurement. Another detail for testing that’s worth mentioning
is that once a barrel was installed on the Unlimited rifle, I fired a series of five-shot groups with a specific lot of Lapua Midas Plus ammunition, checking to see if the barrel was installed correctly. I already had tested the ammunition in a few different Benchrest rifles and it had proven to be very consistent in velocity and highly accurate. While these were new barrels with sporting chambers, as well as not having the benefit of tuners, I still found an acceptable level of ac- curacy (roughly a 0.4" average at 50 yards) from both when shooting the Lapua control ammunition. I also thought it important to shoot the two new
Chamber Differences Page 68 Spring 2013
Lilja barrels before I used them for the test. After they were cleaned and installed, I fired 200 rounds of CCI Standard Velocity through each barrel, cleaning out the barrels after every 50 rounds. I cleaned the full length with TM Solution and Kroil using a stainless steel Ivy rod, as well as using a
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