Eurooptic vortex burris nightforce sale

teslong borescope digital camera barrel monitor

As an Amazon Associate, this site earns a commission from Amazon sales.

July 4th, 2021

Sunday GunDay: 6mm CM and 6.5 CM Switch-Barrel PRS Rig

Zero Compromise ZC517 FFP scope PRS shooting

Today we feature a modern switch-barrel PRS chassis rifle set up for quick changes between 6mm Creedmoor and 6.5 Creedmoor barrels. The owner, Forum member Jeff Cosgrove (aka “Punkur67″) uses the 6 CM barrel for competition, favoring the reduced recoil over its 6.5 mm big brother. He does use the 6.5 CM barrel for practice (given its better barrel life). The 6.5 CM barrel also gives him the chance to shoot a variety of factory 6.5 Creedmoor ammo.

- Terminus Zeus action with Quick Change (QC) barrel option.
– 6mm Creedmoor Pre-Fit Bartlein Heavy Varmint 400MODBB barrel for matches
– 6.5 Creedmoor Pre-Fit Benchmark Heavy Palma barrel for training
– MPA BA Competition chassis with full weight kit
– Zero Compromise Optic ZCO 5-27x56mm FFP scope
– TriggerTech Diamond trigger

This rifle represents an evolution for Jeff. Each step along the way in his PRS journey, he has learned more about what he wants and needs in a competition rifle. And what you see here, from the $3760 ZC527 scope to his high-tech reloading equipment, represents pursuit of excellence. Jeff even created a modern, spacious man cave/reloading center in his new house (photos below).

Zero Compromise ZC517 FFP scope PRS shooting

Quick-Change Barrel System with Terminus Zeus QC Action

Terminus Zeus QC action scope PRS shooting

This rifle has two pre-fit barrels that work with the Terminus Zeus QC Action for fast and easy barrel swaps. To remove a barrel, you simply release two tension screws on the front of the action and then unscrew the barrel. To swap in a different pre-fit barrel, reverse the process and then tension the screws. The Terminus Zeus is 3-lug receiver with 60° bolt and integral recoil lug. Both the receiver and bolt are DLC-treated. Jeff reports this action is extremely smooth and has met all of his expectations. Some other Zeus features are threaded trigger pins for quick/easy trigger installation, and a roller-tipped cocking piece.

PRS Discipline Offers Fun, New Challenge for Long-Time Shooter

Zero Compromise ZC517 FFP scope PRS shooting

My name is Jeff Cosgrove, I live in Winchester, California and do commercial heating and air conditioning. I have shot for 20+ years but I found my interest in shooting was dwindling over time. I got somewhat bored with shooting paper at 100 yards or plinking cans out in the desert. About 18 months ago I decided I wanted to shoot long range. I picked up a used MPA in .300 Winchester Magnum and started shooting long range with a new buddy. That day I fell in love with guns all over again with more intensity than ever.

How I Got Started in PRS
With that new .300 WM I soon found my reloads were not up to my expectations (high ES/SD), so I purchased all new reloading hardware. One of my purchases was a used Benchsource Annealer. The guy I bought that from asked if I had ever tried PRS and he invited me to check out a match. So I went to a local PRS event as a spectator. I looked at many rigs on the firing line and took notes. By the end of the day I knew this was something I really wanted to do. I then acquired a used chassis rifle that I thought would work well for PRS. I went to a PRS match the following month but shot poorly.

After working with that first PRS rifle, a 6.5 CM with Stiller Tac30 action, MDT chassis, and Proof Carbon-wrapped barrel, I quickly learned that gun did not handle and balance the way I hoped.* It was too light in the front, the ergos were poor, and scope eye relief was not optimal. So I decided to build my own GEN 2 PRS rifle. This is the story of how I put together my new switch-barrel rig that I now use in competition.

PRS Rifle and Gear Selection — Learning What Works

Barrel availability was limited given the current shortages. Luckily I was able to obtain a 6mm Creedmoor pre-fit Bartlein Heavy Varmint 400MODBB from Southern Precision Rifles. The 6mm Creedmoor is notorious for being a barrel burner cartridge so I went with the special 400MODBB metal. Bartlein says that barrel life expectancy is 1.5 to 2 times longer than the standard 416 grade steel. I also purchased a 6.5 Creedmoor pre-fit Benchmark Heavy Palma barrel for training (Source: Straight Jacket Armory). With the Terminus Zeus quick change system I am able to swap from my match barrel to my trainer barrel in just a couple minutes. I loosen two set screws, unthread the barrel, thread the new barrel on, and torque the set screws to 10 inch-pounds. This also affords me caliber options in case I’m in a pinch for ammo. If I have some 6.5 CM loaded up and don’t have time to load 6mm Creedmoor for a match, then I’m covered.

For the trigger, I went with a TriggerTech Diamond Pro curve model. I have Timney, Jewell, and TriggerTech triggers in other rifles. I like them all but I liked the feel of the TT Diamond the best so that is what I used on this build. I set my triggers around 18-20 oz. — I am not a fan of ultra-light trigger pulls.

MPA BA Competition Chassis with Added Weight
I went with an MPA BA Comp chassis with full internal and external weight kit. I also have Gray Ops external weight on the handguard. I had the same chassis on my .300 WinMag and felt very comfortable with it. I took a PR1 class and found that, with a different gun, I had to force a comfortable hand position for proper trigger pull. After that class I grabbed my MPA and my hand fell in to the perfect position. I did not need to hunt or index my hand with the MPA. The built ARCA rail (RAT) lowered the rifles center of gravity more than my old setup with the ARCA rail bolted to the bottom of the handguard. With the current configuration, the rifle weighs in at 24 lbs. and balances three inches in front of the magwell. I now have the flexibility to add, subtract, or move approximately 6 lbs. of weight.

The Attraction of PRS/NRL Practical Competitions
I really enjoy PRS-style shooting because there seems to be a new challenge every time you compete — no matter what. With PRS I am shooting many different positions and ranges with the pressure of a stopwatch. This keeps things interesting for me. I have taken a few training classes to help establish good, clean fundamentals.

Zero Compromise ZC517 FFP scope PRS shooting
Jeff says it is hard to practice for the many unconventional shooting positions at PRS matches.

My biggest challenges so far have been: 1) building stable shooting positions that I have not practiced enough; 2) proper equipment selection; and 3) time management. Regarding the shooting positions — PRS/NRL is not like F-Class where you can always practice from one position. And it’s hard to practice for unusual set-ups (barriers and positions) you’ve not encountered before. Concerning equipment — you need some experience in the game to determine what really works best for you.

Innovative Zero Compromise Optic — Optimized for the Tactical Game
Zero Compromise ZC517 FFP scope PRS shooting
The scope is a Zero Compromise ZC527 (5-27x56mm FFP) with MPCT2 reticle. Zero Compromise Optic is a relatively new manufacturer, but their scopes are top-flight. The First Focal Plane ZCO has excellent glass that is extremely bright and clear. With a big 36mm main tube, the ZC527 offers 35 Mils Elevation and 21 Mils Windage adjustment. The field of view is 21 feet at 100 yards — one of the widest in the industry. The ZC527 also offers illuminated reticle and locking turrets. When I was at my first PRS match I looked through several different scopes. When I got behind a ZCO scope I knew this was what I wanted — the ZCO scope was super clear, super sharp, with very positive controls.

I put a protective wrap on the scope because with some of our PRS stages it is easy to scratch or dent the scope tube. You don’t want to bang up an expensive scope — the ZC527 retails for $3760.

Reloading for 6mm Creedmoor and 6.5 Creedmoor

When starting out with a new cartridge I like to search places like and for popular recipes used by knowledgeable shooters. I am all about paving your own way on certain things but with the consistency, higher cost, and limited supply of components these days I try to stick with the most common loads. I also want to limit barrel wear and get through load development quickly. I don’t want to chase loads for 300 rounds to ultimately land in the same place that so many other people have already found.

6.5 Guys load development Spreadsheet excel PRS shooting

I start my new barrels with virgin brass and load three rounds at each charge weight in 0.2 grain increments. I put the most popular charge weight (for my chosen bullet) in the middle of my load range and load above and below to find a good node while paying close attention for pressure signs along the way. I use the 6.5 Guys spreadsheet (see below) to help analyze my results. With those results I like to re-test a narrower range with 5-10 rounds each charge weight in 0.2 grain increments. I again use the 6.5 Guys spreadsheet to make a final charge weight selection and then I move on to seating depth. I will load different depths to tighten the groups up.

6.5 Guys load development Spreadsheet excel PRS shooting

Load Development Using 6.5 Guys Custom Spreadsheet

To hold and analyze my load development data I use the spreadsheet from It helps a ton with making a decision on your final load. This Excel spreadsheet works great and makes it simple to analyze your data. You can even copy and paste your chronograph data if your chrono logs on to a SD card.

6.5 Guys load development Spreadsheet excel PRS shooting

In this 6.5 Guys video Steve provides an overview and tutorial for using the Excel load development analysis model that he has developed. The Excel Load Development Analysis Spreadsheet version 2.0 is FREE. Download from the 6.5 Guys Website.

In this video Steve explains some key statistical concepts for performing load data analysis. He also provides tips and guidance for determining the optimal load for your rifle as you analyze the load data you’ve collected.

New House, New Man Cave/Reloading Room

Jeff recently moved with his family into a great new house. One bonus of this move was that he upgraded from a cramped reloading area to a dedicated “Man Cave” that has ample space for his gun safes, multiple presses, and all his reloading components. Large upper and lower cabinets plus a dedicated “gun closet” provide plenty of storage. Read all about this move in this AccurateShooter Forum Thread.

Here is Jeff’s first reloading area years ago: “My first reloading setup was smashed in my two-bedroom condo so I had a very small bench that was very cluttered. I had to deal with the limited space I had but I made it work. Then in our first house I had a larger bench/cabinet, but it was still not ideal.”

6.5 Guys load development Spreadsheet excel PRS shooting

Here is the new Man Cave in the new house — very open, spacious, with plenty of storage.

6.5 Guys load development Spreadsheet excel PRS shooting

This animated GIF shows the new Man Cave move-in process start to finish:

new reloading bench 6.5 Creedmoor


Permalink - Articles, - Videos, Competition, Tactical, Tech Tip No Comments »
July 4th, 2021

Will Carbon Build-Up Inside Cases Raise Load Pressure?

Carbon fouling case cartridge interior Pressure volume ultrasonic

As a cartridge case is reloaded multiple times, burnt powder residue and carbon builds up on the inside of the case. Unless the case interior is cleaned in some fashion, eventually you’ll see a slight reduction in case capacity. One of our Forum members from Australia wonders about the effects of reduced case capacity: “If the capacity of the case decreases as the crud builds up, then it effectively reduces the size of the cartridge (inside). Wouldn’t that change the pressure produced from that of an equivalent clean case?”

Interesting Test of Case Capacity Changes
Forum member Fred Bohl has actual test results that can help answer the above question. Fred proved that, over a 20-reload cycle, the case capacity of uncleaned cases did decline a small amount. However, surprisingly, this did not seem to affect the actual chronographed velocity of the load. Extreme Spread (ES) did increase, but Fred believes the higher ES was due to changes in case-neck tension, rather than due to the slight reduction in case capacity. Fred reports:

“Back when beginning to use ultrasonic case cleaning, part of the motivation was to get the inside clean based on the assumption that allowing burnt residue to build up inside cases would affect capacity, and, ultimately, performance. An experiment was done to test this hypothesis. The load used, 30.5 grains of RL15 behind 107gr SMKs in a 6mmBR, was selected for best group and lowest ES in prior load development. It turned out to be 92% of initial case capacity and neither “full” or compressed. (I would suspect that different powders, load weight, and total case capacity might produce very different results.)

We took 30 cases of identical initial capacity and tracked three lots of 10 each:

LOT 1: No Internal cleaning
LOT 2: Cleaned with media in tumbler
LOT 3: Cleaned with Ultrasound machine

Each case (in each lot) was shot and reloaded 20 times. The simplified results after 20 reloads of each lot were as follows:

Lot 1 (not cleaned) – 0.3 to 0.4 gr. loss of capacity, 5 to 8 fps greater ES.
Lot 2 (tumble cleaned) – 0.1 to 0.3 gr. loss of capacity, 4 to 6 fps greater ES.
Lot 3 (ultrasonic cleaned) – no loss of capacity, no detectable change in ES.

There was no detectable correlation of velocity change to the lots. An oddity was that on very hot days Lot 1 velocities were, occasionally, slightly higher. From results of another ongoing test, I believe the above differences in ES are probably due more to variance in bullet grip tension than case capacity. The ultrasound cleaned cases (LOT 3) did maintain the lowest ES, but we are not 100% sure of the reasons why. More consistent bullet seating might be the reason.”

Carbon fouling case cartridge interior Pressure volume ultrasonic

Editor’s NOTE: Fred’s results do suggest that carbon build-up inside the uncleaned cases might cause a slight increase in pressure that shows up on hot days. Fred has posted that: “A local shooter reported doing the 20 reload, no-clean test on a .308 that gave a loss of capacity of 2.0 grains, doubled ES and significant velocity changes. However, I don’t have any details on his load weight or powder.” Obviously a lot of carbon can build up with 20 reloads. Many shooters retire their brass before then.

Ultrasonic Cleaning and Neck Lube
Some time ago, Jason Baney did a lengthy test on ultrasonic cleaning. Jason found that with his ultrasonically-cleaned cases, the inside of the necks got so “squeaky clean” that he needed to use dry lube in the necks. Jason uses the $10.95 dry lube kit from This applies ultra-fine Moly powder to the neck using small carbon steel balls. moly neck lube

Permalink Bullets, Brass, Ammo, Reloading, Tech Tip 3 Comments »