The Vector Arms V51SBR: Big Performance, Small Package
Text & Photos by Jeff W. Zimba

Vector Arms is known industry-wide for their Uzi line. In the last few years, this company has added several products to their repertoire, most noticeably their line of HK style weapon designs. Their innovation in this area continues.

In the March, 2005 issue of Small Arms Review (Vol. 8 No. 6) we tested the Vector V53 SBR as well as a few other exotic HK clones. We were quite impressed with this .223 and were anxious to request a sample of the big brother in the .308 NATO caliber (7.62x51mm) V51SBR for evaluation as soon as its addition to the production line was announced. Upon their initial production release we received this sample for testing.

Built on the receiver of an original PTR-91 by J.L.D. Enterprises, the Vector Arms V51 looked promising right out of the box. Expectations were very high on this rifle because of the extreme satisfaction encountered by the V53 we tested. Vector Arms did not disappoint. The V51SBR sent for evaluation was fitted with a 3-position metal lower for aesthetics, even though it only supported a semiautomatic trigger pack. The ears have been left intact giving a look similar to a swing down gun, and with the users addition of a few front pin parts and the tactical application of some strong glue, the look can be completed. A paddle magazine release has also been added, easing the change of magazines and also contributing to the more traditional look of the factory H&K full automatics.

The furniture shipped on the V51 is a standard MP5 length front handguard and what appears to be a standard full-length rear stock. A quick peek inside the stock will reveal that the bolt return spring is far from stock or standard and is a highly modified proprietary upgrade of the Vector V51. One of the necessary modifications to the 51-length guns was the shortening of the recoil spring guide rod to accommodate the shortened action of the recoil system. A negative symptom of this necessary modification was often the weaker return power of a now shortened return spring. Vector has solved this by designing and including a retractable, piston style spring guide rod, allowing a full length spring to be utilized, therefore providing the necessary force to strip rounds and lock up properly.

The finish on the V51 is a dark, black powder coat, matching perfectly between the receiver, the trigger group and the metal on the stock. Everything looks like it belongs together, not simply assembled from an inventory of spare parts.

Smooth Operator

The action is smooth to operate and the camming action of the non-reciprocating cocking handle completely unlocks the locking piece in the bolt, making rearward travel effortless compared to several others we have tested in the past. The heart of the recoil system of the H&K guns and these similar designs is the locking piece. The system of operation in these guns is a delayed blowback, roller lock bolt system. The locking piece is manufactured with different angles that determine how long the action stays locked up, before allowing the rollers to unlock the bolt, and start the action opening and rearward travel. The angles on the locking piece are determined by several factors, including the ammunition used and the length of the barrel. If the locking piece allows the action to open too quickly after firing, the recoil is often quite excessive and can be heavy enough to actually damage the firearm. If the action is allowed to stay locked up too long and open later than necessary, it can result in a short stroke and create problems with ejection and feeding. If you have fired a firearm in the HK family and noticed either of these undesirable symptoms, utilizing the correct locking piece may have possibly been the cure - or at least a large part of it. Vector has done a lot of trial and error testing in respect to the correct locking piece angles and it was obvious the first time we squeezed the trigger. The recoil is minimal, the gun is controllable and the function is excellent. They are using a custom ground locking piece in their V51 with a non-standard angle they developed particularly for this system. This is a basic explanation of the function of this complex system and if you would like to read a little more about locking pieces and their uses, the January 2001 issue of Small Arms Review had a very thorough article and pictorial including a chart of known angles we have encountered.

Bigger Is Not Always Better

The V51 is a much smaller package than the full size rifle it started life as. In this case, the full length PTR-91 as manufactured by JLD Enterprises comes in with an overall length of 40 inches with a 22.52-inch sight radius and weighs 9.17 pounds, empty. Compare those numbers with the Vector V51SBR at 31.5 inches in overall length with a 16.5-inch sight radius. Unloaded weight is still 8.07 pounds so it still carries some of the heft that allows a rifle chambered in 7.62x51mm to be as controllable as possible. The overall length of either of these firearms can be reduced drastically with the addition of the A3 collapsible stock instead of the full-length stock. The most noticeable difference between the stock PTR-91 and the Vector V51 is the length of the barrel. The PTR-91 comes with an 18-inch barrel and a 16-inch barrel on the PTR-91K. The vector V51SBR sports a 9.5-inch barrel. For those individuals who can not own a short barrel rifle, a 16-inch version is available at no additional fee.


While it is obvious that a barrel as short as those in the V51 lose some muzzle velocity compared to their full-length counterparts, we decided to find out exactly how much difference there really was. It seems that the number of 2,500 to 2,600 feet per second seems to be the benchmark when discussing 16-18 inch barrels with standard 150-grain .308 NATO ammo. With those numbers in mind, we setup a PACT MKIV Chronograph, 8-feet in front of the muzzle of the Vector V51 and recorded several data strings with several types of ammunition. The complete chart is shown, but as a summary of the four types of ammunition used, the average velocity was 1,964 fps with a consistency averaging 59 fps in variance between extreme high and extreme low speed. The best consistency we recorded was using the new 150-grain WOLF Gold SP ammo with an extreme spread of only 21 fps. It beat the second best, which was M118 Lake City Special Ball ammo, which had an extreme spread of 52 fps - double that of the WOLF Gold. The fastest we recorded was with the M1A2 Portuguese Ball ammo, which averaged 2,056 fps with the M118 Lake City Special ball coming in last, averaging 1,923 fps. All shooting was done off hand with the 4-position peep-style diopter sight at 50 yards and 100 yards. While all hits with all ammo were sufficient in placement for "kill" shots utilizing standard B27 silhouette targets, there was no noticeable difference between any of the brands in grouping. No testing was done with use of a bench rest or optics of any type.

For an attention getter, we have to recommend the Wolf 150-grain FMJ ammo. When we switched to this ammo for testing, the sound was a little louder, which a V51 is notorious for, and both the muzzle flash and muzzle blast was much more intense than with the other test ammunition. Every time a round was fired the chronograph screens would flex. This round of testing actually worked out to be an endurance test for the PACT IV Timer and Chronograph and we are extremely pleased to report that it passed with high honors and stayed in one piece.

Ready to Rock

Any configuration in the V51 series of firearms from Vector should make the owner of a registered sear or trigger pack a very nice host gun. The bolt carrier supplied with the firearm is ready to facilitate a pack or sear. The test sample we utilized for this evaluation was fitted with two different, registered trigger packs and with a minimal amount of position adjustment it ran as well in semiautomatic as it did in full automatic. Because of all the differences in trigger packs, shelf heights, and types of conversions available, it is necessary to find the right combination of trigger group and lower to properly fit the firearm at the right height to ensure the correct timing. The V51 can be currently ordered as a Short Barreled Rifle as tested, requiring a $200 transfer tax, as a pistol with no stock and no transfer tax necessary, or as a Title 1 firearm with a muzzle extension to 16 inches, also requiring no transfer tax.


The Vector V51 is going to make many shooters and collectors of these "exotics" quite happy. With a high quality fit, finish and function combined with excellent controllability and a retail price under $1,000, these guns also provide an excellent host for registered sears and trigger packs. They also make a fun gun in their original semiautomatic configuration. The noise and muzzle flash of a 51 is something not comparable with many other small arms and is one gun sure to gather attention at any shooting range. Vector did a great job with this project and their version is among the best of the best in every aspect.


Caliber: 7.62x51mm
Overall length: 31.5 inches
Barrel length: 9.5 inches
Barrel, rate of twist: xxxxxxxxxxx
Sights, front: Fixed post in ring
rear: 4-position, peep-style rotating diopter
Sight radius: 16.5 inches
Weight, unloaded: 8.07 pounds
Method of operation: Semiautomatic, delayed blowback roller lock bolt system
Magazine capacity: 20 rounds
Finish: Black powder coat
Manufacturer: Vector Arms, North Salt Lake, Utah
Retail price as tested $954

Vector V51 Muzzle Velocity

Portuguese M1A2 Ball
Wolf 150-gr FMJ Ball

Wolf Gold 150-gr SP

Lake City

M118 Special Ball

Average Muzzle Velocity
2,056 fps
1,933 fps
1,944 fps
1,923 fps

Extreme Spread
88 fps
78 fps
21 fps
52 fps


Vector Arms
Dept. SAR
270 W. 500 N.
North Salt Lake, UT 84054
Ph: (801) 295-1917
Fax: (801) 295-9316

Wolf Ammo
Wolf Performance Ammunition
Dept. SAR
1125 N. Lance Lane
Anaheim, CA 92806
Ph: (888) 757-WOLF
Fax: (714) 632-9232

PACT Timers
Dept. SAR
P.O. Box 535025
Grand Prairie, TX 75053
(800_ 722-8462