February 5th, 2019

Blast from the Past — 6mmBR Drop-Port Viper

This week we return to our 6mmBR.com roots with an article on David Bergen’s slick 24″ Drop-Port Viper. This was one of the first 6BR rifles we featured. David, who hails from Belgium, developed this project over many months, and the gun proved to be a true tack-driver, with the ability to group in the Ones, even with the heavy boat-tail bullets. David talks about the build and his reloading methods while action designer Jerry Stiller provides technical insights into the design features of his Viper action.

Report by David Bergen

It was a long journey looking for the perfect custom action to build my new rifle. I searched the internet and visited various forums. I even re-read all my old Precision Shooting magazines to find what I was looking for. One evening I conferred by telephone with Mr. Jerry Stiller of Stiller’s Actions in Texas. He patiently answered all my questions. That moment I decided that I wanted a Viper Drop-Port action. [Editor: Sadly, the Viper Drop-Port is no longer in production.]

Component Selection
At the heart of this gun is a Viper action. This medium-sized action can handle cartridges from a small BR up to a 6.5-284. (Stiller’s smaller Cobra action is for PPC and BRs only.) The Viper is milled from aluminum. This keeps weight down while still allowing Vipers to have a large bedding surface like a Stolle Panda.

Viper Drop port action

At first I was a bit sceptical about the aluminum’s toughness, but Mr. Stiller informed me that the action is the perfect marriage between steel and aluminum. The bolt is hard-chromed and the action body is hard-anodized. This gives it two surfaces that resist wear and make an already-slick action even slicker. Stainless steel is used for all the heavy-stress points including barrel threads, locking lugs, and the rear camming surface. The bolt is made of steel with a very light, small-diameter firing pin to prevent primer piercing with heavy loads. Everything is held very concentric to the bore axis. The Viper is a very smooth action mainly because the design and the precise machining of the camming surfaces. Combined with optimal bolt-lift timing, this gives a smooth action. Stiller also keeps the tolerances very tight on these actions, though they are as fast-handling as any you can buy. The trigger is of course a Jewell BR model.

The rifle is chambered in 6mmBR Norma, my favorite cartridge. I have two HV-contour Shilen match barrels, both with 1 in 8″ twists and finished lengths of 24 inches. The chamber has a .266″ neck so neck-turning is necessary. Freebore is .060″ but combined with a 1.5° throat angle this lets me seat a wide range of bullets from 58 grains up to 107 grains.

The stock is a McMillan Edge with moulded-in gray and black marble swirl. I specified 60% black and dark and light gray both at 20%. I went with the Edge stock because I was always pleased with McMillan products and because it had a very low center of gravity. I wanted the barrels very low in the stock because I think it makes the gun track better.

Details of the Drop-Port–with VIDEO!
The visible part of the Drop-Port is a cartridge-sized cut-out in the floor of the action. This tapers into a funnel shape that lets the spent case fall nose-first through a single hole in the underside of the stock. The Drop-Port is carefully sized so that empty brass will fall through from gravity but a loaded round won’t. I’ve found that getting a BR case to eject 100% reliably in a standard action is not easy. The round is short and fat so it clears the chamber too early and the ejector pushes the cases out the extractor too fast. This can result in an empty case sitting in your action, no longer held by the extractor. Needless to say, this can slow you down during a stressful competition. When you get a Drop-Port you can forget all those problems.

Failure to eject is NOT going to happen with a Drop-Port. The system just works every time, and it’s FAST. Right-Click on the Media Player image and “Save As” to download a video (6.9 megs) showing me cycling the action during live fire.

One smart feature of the Drop-Port is the extractor location. A Remington extractor is located at the bottom of the bolt. This way the case is supported by the extractor until the front of the case lines up with the cut-out in the action. At that moment the front of the case tilts down and the rim slips out of the extractor. In the stock there is a funnel which collects the case. The case drops out of the rifle through a single small hole in front of the trigger guard.

Building an Accurate Load
Tools and Recipes

I start with new Lapua cases and after full-length sizing I trim them with a Wilson trimmer. Then I turn the necks for a .264″ neck diameter with a Lapua 105 seated in the brass. After fire-forming I use a “semi-custom” Harrell’s full-length sizing die with bushing. I use a .262 bushing with the moly-coated bullets. This Harrell’s die is the best I ever used — it gives very low run out. [Editor’s Note: Harrell’s stocks a number of dies with various internal dimensions. You send them three fire-formed cases and they’ll pick out a die that fits your brass the best. The cost is very reasonable.] Overall the excellent concentricity I’m seeing with my rounds is a combination of a superb chambering job, a neck-turned Lapua case and the Harrell’s sizing die. The die is supplied with a brass bushing that allows you to measure the amount of sizing you are doing.

For seating I use both a Wilson inline seater (hand die) and a Forster seating die that threads into a press. The latter gets the most use because I find it easier to use. Run out with both is around 0.001″ or better measured on the bullet.

Load development was very easy. I started with Varget and all loads … shot well. Vihtavuori N150 also shot very well with… moly-coated Lapua 105s. To my delight, the light bullets are also shooting very well in the 1:8″ twist. Nosler Ballistic Tips are giving very good results with a case full of N140. I’ve also tried N150, N540 and AA 2520. For all loads I’ve been using CCI BR4. Bullets are seated well into the lands with square marks showing. This gives an overall length around 59 mm (2.32″), depending on the bullet used.

Shooting the Rifle–How It Performs
The rifle is very easy to shoot and it is very accurate, but it had some drawbacks in the beginning. First there is the stock. It is designed for bench shooting and on a table it does this very well. I use a Caldwell front rest and a Protektor rear bag. When shooting prone I’ll also use the rest but the cheek weld is not ideal (the Edge was optimized for free recoil shooting from the bench). The rings that are supplied with the action are rather high. I looked around and found some that were lower. This made shooting easier, but I still wasn’t satisfied. The gun was a bit nose-heavy. There is a weight system built into the stock, but it wasn’t enough to bring the gun in balance. I like the balance point to be just in front of the receiver ring. So I cut the rear off the stock and put in a larger tube and turned some weights to put in it. I also made up an aluminum butt plate. Then I installed a Harrell’s brake to cut recoil to a minimum. With these modifications, the rifle is now shooting the way I want. I think the Edge stock is a very good design for benchrest shooting but for prone shooting it has some shortcomings. I think the MBR is a better stock for shooting prone.

Muzzle Brake–Less Recoil, Same Excellent Accuracy
After testing the barrel with different loads, I decided to put a brake on one barrel. Most of my guns are muzzle-braked and since I had two virtually identical barrels, I put a Harrell’s brake on one. The barrel had to be threaded to mount the brake and here I was a little concerned–I remembered the advice to “never mess with a winner”. The un-braked barrel was ultra-accurate and I was curious whether the process of fitting the brake might affect the accuracy.

Thankfully, my worries were unfounded. My targets showed no loss of accuracy — there was no evidence that the brake had caused any changes (except as to recoil). I have wondered though, perhaps the brake makes the gun more shootable and in that way compensates for some small accuracy loss that may be there? Whatever the case, the gun shoots just as tight as before, except now it’s a lot more user-friendly with less muzzle hop and less “push” on recoil.

This Rifle Literally Shoots Bug-Holes
And now I come to the end of the story. One day when testing the rifle at 100 meters (with brake installed), I spied a fly on the target. Well now, I thought, here is an interesting “precision shooting” challenge. I put the crosshair on the fly, squeezed the trigger, and the fly was history.

One shot, one kill. Now THAT is impressive precision. If you look closely you’ll see what’s left of Mr. Fly around the bullet hole. Or “bug-hole” as you Americans would say. This kind of performance is a real confidence-booster for the trigger-puller, let me tell you.

The Drop-Port — Simple Yet Advanced
Jerry Stiller tells us: “The drop-port ejects the case out the bottom of the action using only gravity. No ejector plunger is required so the system is as foolproof as anything can be. (A normal spring-loaded ejector creates an uneven load on one side of the case head.) Unlike other ejection systems, micro-ports etc., a Drop-Port doesn’t require tuning or adjusting, and just works. Many top shooters tell us they can cycle rounds faster with a Drop-Port action than with any other design.”

“The engineering of the Viper reflects some key design objectives. I wanted it to be able to fit standard commercially available stocks and have a barrel fit-up that was well known in the industry. I liked the idea of the larger bedding area and higher stiffness of the aluminum actions, so I chose the Panda footprint and barrel tenon for the Viper. I also made some changes to what was available at the time to make the product better. I used a smaller diameter firing pin to eliminate primer piercing, hard anodized all the aluminum parts for corrosion resistance and to make the surface hard and slick. The bolts are also coated for the same reasons.

Drop-Port technical drawing, Copyright © 2005, Stiller’s Precision Firearms, All Rights Reserved.

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July 18th, 2011

Leo Anderson Smashes 1000-Yard Score Aggregate Records

Leo Anderson 1000 yard recordMontana 1K benchrest shooter Leo Anderson has set a pair of astounding multi-match Light Gun Score Agg records. These are “records for the ages”. This season, Leo’s 6-match Score Aggregate was 99.5 (99,99,99,100,100,100), while his 10-match Score Aggregate was 96.8 (84,94,95,98,99,99,99,100,100,100). That’s amazing consistency. Given how hard it is to shoot a single 100 score at 1000 yards, Leo’s Aggs are jaw-dropping. It will be a long time before these Agg records are broken (if they ever are). Leo set his 99.5 (6-match) and 96.8 (10-match) records shooting a 17-lb rifle chambered for the 6mm Dasher. The Lawrence barrel was chambered by Montana gunsmith John King and Leo did the stock work himself (starting with a Shehane MBR Tracker).

Leo Anderson 1000 yard record

99.5 Six-Match Agg and 96.5 Ten-Match Agg at 1000 Yards
Leo set these multi-match Agg records at the Deep Creek Range near Missoula, Montana. Tom Mousel, another record-holding Montana shooter reports: “Our Agg season is now complete here in Montana. Leo ‘Legend’ Anderson has broken both the 6-match and 10-match score aggregate records. He hasn’t just broken them, he has smashed them, with a couple Aggs that are truly remarkable. As a fellow 1000-yard competitor, I fully understand what it takes to grind out a quality Aggregate. What Leo has done this year is the most impressive thing I think we might ever see in the 1000-yard benchrest game. Leo is one of the best of the ‘good guys’, and also, in my opinion, Leo is the best 1000-yard shooter to ever grace our sport. You’d have to check with Leo, but I believe these are his 14th and 15th world records in his career. Leo also holds our Club record for Light Gun group and score, when he drilled a 3.476″/100 back in August of 2008″. (See photo below)

Leo Anderson 1000 yard record

Record-Breaking 6mm Dasher Light Gun Specs
There’s nothing really exotic about the 17-lb Light Gun with which Leo set his score records. The stock is a laminated Shehane MBR Tracker with some modifications by Leo to make it track better. Leo altered the angle of the toe to match the forearm and modified the taper of the sides of the buttstock to ride better in the bags. Pillar-bedded into the stock is a Stiller Viper Drop Port. Leo loves this action. He says it is very fast to operate and the flat bottom makes it easy to install in the stock. In addition, the Viper action works well with his preferred CCI 400 primers: “I can run stout loads of H4895 with the Viper without cratering the primers. Some guys with other factory and custom actions have problems with the CCI 400s which are not as hard as the 450s.”

The 29.5″, 5-groove, 0.237″ land, HV-counter barrel was crafted by Lawrence Barrels. Based in Lewiston, Montana, Lawrence Barrels currently makes mostly AR barrels, but Leo says they make great cut-rifled tubes: “I currently have Lawrence barrels on both my Light Gun and my Heavy Gun. These Lawrence barrels both shoot great. I think they are the equal of the best examples from top barrel-makers such as Krieger and Bartlein.” Leo has tried straight-contour barrels, but he prefers some taper (similar to a Krieger #17 contour): “In my experience, tapered barrels seem to shoot better, at least in a 17-pounder. The gun is less nose-heavy and tracks better.” The barrel on Leo’s record-setting Light Gun currently has about 900 rounds through it.

For optics, Leo runs a 12-42x56mm Nightforce BR model with NP2DD reticle. Leo tells us: “the NP2DD reticle is my favorite and I have great confidence in the Nightforce. We tried it side-by-side with a big name European-made high magnification scope, and the Nightforce was visibly better. At 1000 yards it had better clarity, better sharpness, better resolution.”

Record Setting Dasher Recipe: Berger 105gr VLD, Hodgdon H4895, CCI 400, Lapua Brass
While many top 6mmBR and Dasher shooters use Varget or Reloder 15, Leo prefers Hodgdon H4895, which has a slightly faster burn rate. Leo tells us: “Right now, the H4895 and CCI combo is giving the best accuracy, and it’s a clean combination. I’ve shot a lot of Reloder 15, but the H4895 burns so much cleaner.” Leo’s load is running around 3050 fps, but “he’s not too concerned with what the chronograph says — when we tune our loads we go by what shows up on the target.” Leo is loading a bit more than 32 grains of H4895. (Editor’s NOTE: This load is for fully fire-formed Dasher cases ONLY. It is NOT safe to use in a 6mmbr with 105s.) Leo’s favorite projectiles are the “thin-jacket” Berger 105gr VLDs, pointed with a Whidden pointing tool. Leo turns his necks with a K&M neck turner.

To save on barrel life, Leo fire-forms his brass using a separate barrel. He prepares the brass with a false shoulder, then fires the cases loaded with pistol powder, cream of wheat and low-density plug in the end. He tried forming case with pistol powder alone, but that required much more powder and didn’t produce results as good as the cream of wheat method.

Shooting Fast — the Importance of Smooth Tracking
Leo tells us that you need a great-tracking rig to be competitive in the 1K game these days: “Some guys are getting 10 shots downrange in 20 seconds or less. It takes me about 30 seconds.” To shoot that fast, the gun needs to track perfectly so you can just slide it back and stay on target. “If you want to shoot fast, everything’s got to be working right — and your stock really needs to track well. If you’re chasing the knobs on your rest, you’re not getting [your bullets] down range.” Leo says the stock’s geometry must be “near perfect” in order for the gun to come back to the same spot shot after shot.

Leo Anderson’s Advice for New Long-Range Shooters.

We asked Leo if he had any advice for shooters new to the long-range benchrest game. Here are some of his thoughts:

1. Pick a Winning Cartridge – Leo thinks the Dasher is just about perfect for a 17-lb rifle: “Any more cartridge than that, you have too much gun movement. Something in the Dasher range is the perfect size. We shoot the Dashers around the 3050 fps node. Even with the 6-6.5×47 you’re just burning more powder, and at the higher node, the gun starts rocking and things start getting away from you.”

2. Get Good Equipment Right from the Start – “Go ahead and bite the bullet and buy good stuff right off. Too many guys try to get off cheap in the beginning. They end up buying two or three guns as they upgrade. You save money in the long run by buying good stuff in the beginning.”

3. Practice, Practice, Practice – “We get a lot of practice in the process of tuning and load development. We put in the time — on things like bullet sorting, case prep, load tuning.”

4. Keep Pushing for Perfection – “A lot of guys get a load that seems pretty good, and then they get lazy. Don’t be content when you get a 6-inch group at 1000, because the gun might shoot a LOT better. I’ve got Aggs in the five-inch range.”

Leo Anderson 1000 yard record
Leo reports: “Here’s our ‘secret’ 1000-yard range out in the sticks where we do some spring tuning”.

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